Prolonged treatment with isoproterenol causes a loss of myocardial Gsalpha mRNA expression.

We investigated the influence of chronic beta-adrenergic stimulation on Gsalpha protein gene expression and beta-adrenoceptor responsiveness in rat ventricular myocardium. The rats received twice-daily injections of 4 mg/kg isoproterenol (ISO) alone or with 8 mg/kg propranolol (PROP) for 4 days. In ventricular myocardium, Gsalpha mRNA expression decreased by 27% after ISO treatment. Dose-dependent (10 nM to 100 micro M) positive inotropic responses by ISO in the left papillary muscles were lower after ISO treatment than in saline-treated myocardium with decreases in ED50 values. PROP itself had no effect, although it antagonized both ISO-induced effects. These results suggest that impaired Galpha mRNA expression may explain the loss of cardiac Gsalpha subunit levels after chronic beta-adrenergic stimulation, and that these changes can provide one mechanism for the progress of long-term desensitization.

Preeclamptic serum enhances endothelin-converting enzyme expression in cultured endothelial cells.

Increased vascular sensitivity to vasoconstrictors, such as angiotensin II and epinephrine, is observed in preeclampsia (PE). Recently, it was suggested that abnormal endothelial function might contribute to the pathophysiologic changes in PE. We investigated vasoconstrictor (angiotensin II and epinephrine)-induced endothelin-1 (ET-1) release from human umbilical vein endothelial cells incubated with sera from women with PE compared with normotensive pregnant and nonpregnant women. Moreover, inositol 1,4,5-trisphosphate production and endothelin-converting enzyme (ECE) expression in human umbilical vein endothelial cells were also evaluated. There were no significant differences in ET-1 release without vasoconstrictors among the three groups (nonpregnant, normotensive pregnant, and PE). No significant differences in basal inositol 1,4,5-trisphosphate production and ECE expression without vasoconstrictors were detected among the three groups. Vasoconstrictor-induced ET-1 release was significantly increased by PE sera. No significant difference was detected in vasoconstrictor-induced inositol 1,4,5-trisphosphate production among the three groups. However, ECE expression after incubation with vasoconstrictor was significantly increased by PE sera. Our results suggest that ET-1 release from endothelial cells may contribute to the increased vascular sensitivity to vasoconstrictors observed in PE, and that vasoconstrictor-induced ET-1 release may be related to enhanced ECE expression.

The relationship between serum nitrate and endothelin-1 concentrations in preeclampsia.

Recently it was suggested that abnormal endothelial function may contribute to the pathophysiological changes observed in preeclampsia (PE). Both nitric oxide (NO) and endothelin-1 (ET-1) are vasoactive substances produced by endothelial cells. NO is a vasodilator and has been believed to be decreased in PE. ET-1 is a vasoconstrictor and has been reported to be increased in PE. We simultaneously measured NO metabolites and ET-1 in sera from women with PE and investigated the correlation of NO and ET-1 concentrations. We obtained serum samples from 11 healthy nonpregnant (NP) women, 16 normotensive pregnant (NTP) women and 17 women with PE. In this study, the serum ET-1 level was assayed by the ET-1 RIA system, and serum NO metabolites were assayed by measuring nitrite (NO2-) and nitrate (NO3-) simultaneously in an HPLC-Griess reaction system. There was a significant correlation between NOx (nitrite + nitrate) and ET-1 in sera from all 44 women (NP, NTP and PE groups) (p<0.001). Nitrite and ET- in sera from each group were not significantly correlated. Nitrate and ET-1 in sera from the NP and NTP groups did not significantly correlate. However, there was a significant correlation between nitrate and ET-1 in sera from the PE group (p<0.05). The serum ET-1 and nitrate concentration in the PE group was significantly higher than in the NP and NTP groups (p<0.05 and p<0.001. respectively). These findings suggest that increased production of nitrate in PE may contribute to homeostatic vasodilation against vasoconstriction caused by a higher ET-1 concentration.

Modulation of phospholipase C pathway in rat cerebral cortex during aging.

The regulation of the alpha(1)-adrenoceptor-G protein-phospholipase C (PLC) cascade was investigated in rat cerebral cortex at adult (6-month-old) and senescent (24-month-old). Norepinephrine (NE)-stimulated inositol 1,4,5-trisphosphate [Ins(1,4,5)P(3)] production was enhanced 30% during aging. Moreover, maximal NE (50 microM) stimulation was much more effective in stimulating G protein low-K(m) GTPase in cortical membranes from old than adult rats. Immunoreactive G protein subunits (Gqalpha, Gialpha, Goalpha and Gcommonbeta) and PLC-beta(1) isozyme were detected in all membrane preparations. No changes in the G protein subunits and PLC-beta(1) expression were observed with aging. Nanomolar concentration of Gpp[NH]p inhibited basal Ins(1,4,5)P(3) production with a maximum inhibition of 25% in both adult and aged cortical membranes. In contrast, 100 microM Gpp[NH]p-induced stimulation of Ins(1,4,5)P(3) production was potentiated with aging. The two principal divergent pathways of old cortical Ins(1,4,5)P(3) production resulting in the activation and inhibition of PLC-beta(1) activity are abolished by treatment of the membranes with 1 microM U-73122, a putative PLC-beta inhibitor. These results suggest that the cortical PLC-beta(1) isozyme activity may be regulated by both inhibitory and stimulatory G proteins-mediated mechanisms, and that the altered PLC-beta(1) dual regulatory systems could be involved in the pathogenesis of brain aging.

Bilobalide prevents reduction of gamma-aminobutyric acid levels and glutamic acid decarboxylase activity induced by 4-O-methylpyridoxine in mouse hippocampus.

We previously reported that bilobalide, a constituent of Ginkgo biloba L. leaves, protected mice against convulsions induced by 4-O-methylpyridoxine (MPN). To elucidate the mechanism of the anticonvulsant activity of bilobalide, this study examined the effect of bilobalide on MPN-induced changes in the levels of gamma-aminobutyric acid (GABA) and glutamate, and in the activity of glutamic acid decarboxylase (GAD) in the hippocampus, cerebral cortex and striatum of the mouse. GABA levels and GAD activity in the hippocampus and cerebral cortex were significantly enhanced by bilobalide treatment (30 mg/kg, p.o., for 4 days) alone. MPN significantly decreased GABA levels and GAD activity in the three brain regions tested compared with those in the control. Pretreatment with bilobalide effectively suppressed the MPN-induced reduction in GABA levels and GAD activity in the hippocampus and cerebral cortex. On the other hand, there were no significant differences in the glutamate levels in the three regions despite various treatments. These results suggested that bilobalide prevents MPN-induced reduction in GABA levels through potentiation by bilobalide of GAD activity, and this effect of bilobalide contributes to its anticonvulsant effect against MPN-induced convulsions.

Propofol-induced depression of cultured rat ventricular myocytes is related to the M2-acetylcholine receptor-NO-cGMP signaling pathway.

BACKGROUND: It is well-known that propofol sometimes causes bradycardia or asystole during anesthesia; however, the direct effect of propofol on the myocardium remains unclear. Previous reports showed the contribution of muscarinic acetylcholine receptors to propofol-induced bradycardia. Conversely, it was suggested recently that nitric oxide (NO) plays an important role in mediating the effect of vagal stimulation in the autonomic regulation of the heart. Therefore, the authors investigated the effects of propofol on spontaneous contraction and NO production in cultured rat ventricular myocytes. METHODS: The authors measured chronotropic responses of cultured rat ventricular myocytes induced by propofol stimulation with a sensor, a fiber-optic displacement measurement instrument. The authors also quantitatively analyzed NO metabolite production in cultured myocytes by measuring the levels of nitrite and nitrate in a high-performance liquid chromatography reaction system. The influence of propofol on muscarinic acetylcholine receptors of myocyte membranes was also measured with a competitive binding assay using [3H]quinuclidinyl benzilate ([3H]QNB). RESULTS: Propofol caused negative chronotropy in a dose-dependent manner. Propofol (IC50) also caused the enhancement of nitrite production in cultured myocytes. Eighty percent of the enhancement of nitrite production induced by propofol (IC50) stimulation was abolished by pretreatment with atropine, methoctramine, or N(G)-monomethyl-L-arginine acetate (L-NMMA). The negative chronotropy induced by propofol (IC50) stimulation was reduced to 40-50% by pretreatment with atropine, methoctramine, L-NMMA, or 1H[1,2,4]oxadiazolo[4,3-alpha]quanoxalin-1-one, a selective inhibitor of guanylyl cyclase. Propofol displaced [3H]QNB binding to the cell membrane of myocytes in a concentration-dependent manner. CONCLUSION: These results suggest that the negative chronotropy induced by propofol is mediated in part by M2-acetylcholine receptor activation, which involves the enhancement of NO production in cultured rat ventricular myocytes.

Capacitative Ca2+ entry involves Ca2+ influx factor in rat glioma C6 cells.

Capacitative Ca2+ entry exists in rat glioma C6 cells; however, how the information of depletion of Ca2+ in intracellular stores transmits to the plasma membrane is unknown. In the present study, we examined whether Ca2+ influx factor (CIF) causes capacitative Ca2+ entry in C6 cells. CIF was extracted from non-treated (Non-CIF), bombesin-treated (BBS-CIF) and thapsigargin-treated (TG-CIF) C6 cells by a reverse-phase silica cartridge. The addition of BBS-CIF and TG-CIF gradually increased cytoplasmic Ca2+ concentration ([Ca2+]i) but Non-CIF did not increase [Ca2+]i. Neither BBS-CIF nor TG-CIF elevated [Ca2+]i in the absence of extracellular Ca2+. Gd3+ inhibited the increase in [Ca2+]i induced by BBS-CIF and TG-CIF. Genistein abolished an elevation of [Ca2+]i induced by BBS-CIF and TG-CIF. BBS-CIF and TG-CIF did not increase inositol 1,4,5-trisphosphate accumulation. The results suggest that capacitative Ca2+ entry is caused by CIF in rat glioma C6 cells.

Effect of chronic ethanol treatment of Ca2+-inhibited adenylyl cyclase in mouse striatum.

In the present study, to investigate the possibility that chronic ethanol treatment might alter Ca2+-inhibited type 5 adenylyl cyclase (AC) activity, we examined the effect of chronic ethanol treatment on striatal dopaminergic signal transduction, especially the AC system, in mice. We fed male C57BL/6 mice for 7 days with a 5% ethanol-containing or control liquid diet. Basal and forskolin-stimulated AC activities were reduced in striatal membranes of ethanol-treated mice. 5'-guanylylimidodiphosphate-stimulated AC activity was also decreased in ethanol-treated mice. But no significant differences were observed in the levels of the guanine nucleotide binding protein subunits Gs alpha and Gi1alpha&2alpha, determined by immunoblotting, between ethanol-treated and control mice. These results indicated that the function of the catalytic subunit of AC was decreased in the straitum of chronically ethanol-treated mice. We further examined the inhibitory regulation of AC activity in the context of a change of type 5 AC. Inhibition of forskolin-stimulated AC activity by 10 microM free Ca2+ was smaller in ethanol-treated mice than in control mice. However, the protein level of type 5 AC in the striatum, determined by immunoblotting, was not significantly different between ethanol-treated and control mice. These findings suggest that Ca2+-inhibited, presumably type 5, AC activity is reduced in mouse striatum by chronic ethanol treatment, and that this reduction is not due to a decrease in type 5 AC expression.

Effects of bilobalide on gamma-aminobutyric acid levels and glutamic acid decarboxylase in mouse brain.

We have previously demonstrated that bilobalide, a constituent of the Ginkgo biloba extract, possesses anticonvulsant activity, and suggested that the mechanism of its anticonvulsant action involves modulation of y-aminobutyric acid (GABA)-related neuronal transmission. This study examined the effects of bilobalide on the level of GABA and glutamate, the activity and the amount of glutamic acid decarboxylase (EC 4.1.1.15), and the function of GABA(A) receptors in the hippocampus, cerebral cortex and striatum of the mouse. GABA levels, glutamic acid decarboxylase activity, and the protein amount of 67 kDa glutamic acid decarboxylase in the hippocampus of mice treated with bilobalide (30 mg/kg, p.o., once a day for 4 days) were significantly higher than those in controls. However, there were no significant differences in glutamate levels or, the number and the dissociation constants of GABA(A) receptors in the hippocampus between control and bilobalide-treated mice. These results suggest that the anticonvulsant effect of bilobalide is due to elevation of GABA levels, possibly through potentiation of glutamic acid decarboxylase activity and enhancement of the protein amount of 67 kDa glutamic acid decarboxylase by bilobalide.

Role of nitric oxide production in carbachol-induced negative chronotropy in cultured rat ventricular myocytes.

It has been reported that nitric oxide (NO) plays a physiological role in mediating the effect of vagal stimulation in the autonomic regulation of the heart. In this study, the changes in NO production induced by carbachol were investigated by measuring the NO metabolites, nitrite (NO2-) and nitrate (NO3-), with a high-performance liquid chromatography-Griess reaction system, and the carbachol-induced chronotropic response was simultaneously investigated. Cultured rat ventricular myocytes exhibited a dose-dependent negative chronotropic response and NO metabolite production in response to carbachol. The negative chronotropy and the enhancement of NO metabolite production induced by 10(-4) M carbachol were completely abolished by 10(-6) M atropine. Both of these effects of carbachol were completely abolished by NO synthase inhibitors such as 3 X 10(-4) M NG-monomethyl-L-arginine acetate and 10(-5) M methylene blue. Furthermore, the negative chronotropic effect induced by 10(-4) M carbachol was also abolished by 10(-6) M 1 H-[1,2,4]oxadiazolo[4,3-alpha]quanoxalin-1-one, a selective guanylyl cyclase inhibitor. In addition, 10(-4) M 8-bromoguanosine 3':5'-cyclic monophosphate, a cell-permeable analogue of guanosine 3':5'-cyclic monophosphate, caused a negative chronotropic effect. These results suggest that the NO-signaling pathway may play an important role in the muscarinic cholinergic regulation of myocardial function.

The direct effect of halothane on myocardial contraction in rat myocytes with poorly developed gap junctional intercellular communication.

BACKGROUND: The gap junction channel plays an important role in synchronous beating in the heart, and the reduction in the amount of gap junctional intercellular communication (GJIC) is thought to be the main arrhythmogenic factor in diseased heart. However, the effect of halothane on myocardial contraction in heart tissue with less GJIC is not well known. The purpose of the present study is to examine the direct effect of halothane on myocardium with poorly expressed GJIC. METHODS: Ventricular myocytes were obtained from neonatal rats by enzymatic digestion with collagenase and then cultured for 3 or 7 d. We have previously reported that the number of gap junctions at 3 d is approximately 10% of that at 7 d (1). The myocytes were stabilized in serum-free medium, and the spontaneous beating rate and amplitude were measured by a fiberoptic sensor. RESULTS: Heptanol (2 mM), an inhibitor of GJIC, abolished synchronized beating in myocytes cultured for 7 d. Halothane decreased the beating rate and amplitude in both groups of myocytes in a concentration-dependent manner (P < 0.05). Halothane at 1 and 2 MAC (adult rat MAC) decreased the beating rate more in myocytes cultured for 3 d than in myocytes cultured for 7 d (P < 0.05). Halothane reduced beating amplitude equally in both groups. Asynchronous contraction developed more frequently among myocytes cultured for 3 d than for those at 7 d. CONCLUSION: Halothane may block the GJIC channels, and when the number of these channels is reduced, exposure to halothane may cause asynchronous beating and decrease the beating rate. However, the halothane-induced decrease in amplitude is probably not due to blockade of GJIC because reducing the number of GJIC channels did not alter halothane's depressant effect.

Effects of bilobalide, a sesquiterpene in Ginkgo biloba leaves, on population spikes in rat hippocampal slices.

The effects of bilobalide, a sesquiterpene isolated from the leaves of Ginkgo biloba L., were investigated in a rat hippocampal slice preparation. Bilobalide (10-500 microM) significantly increased the amplitude of population spikes evoked by electrical stimulation of Schaffer collateral/commissural fibers in a concentration-dependent manner. Paired-pulse inhibition at interpulse intervals of 10-50 ms was significantly reduced in the presence of bilobalide (50 microM). The inhibitory action of muscimol (1 microM) was attenuated by bilobalide (100 microM). These results suggest that bilobalide induces an enhancement of excitability of CA1 pyramidal neurons, which involves, at least in part, a reduction in GABAergic inhibition in rat hippocampus.

Comparative myocardial depression of sevoflurane, isoflurane, and halothane in cultured neonatal rat ventricular myocytes.

UNLABELLED: In this study, we compared the direct myocardial depressant effects of sevoflurane, isoflurane, and halothane and determined whether an L-type Ca2+ channel agonist, Bay K 8644, could attenuate the myocardial depression induced by these anesthetics in cultured neonatal rat ventricular myocytes. Ventricular myocytes were obtained from neonatal rats by enzymatic digestion with collagenase and then cultured for 6-7 days. The myocytes were stabilized in serum-free medium, and the spontaneous beating rate and contractile amplitude were measured by using a fiberoptic sensor. Each anesthetic decreased the beating rate and amplitude in a concentration-dependent manner (1%-4% vol/vol) (P < 0.001), with halothane decreasing the beating rate and amplitude the most (P < 0.01). Isoflurane caused larger decreases in the beating rate than sevoflurane at 3% and 4% (P < 0.05). Potency for suppression of contractile amplitude was in the order of halothane > > isoflurane > sevoflurane. However, the myocardial depressant effects of the anesthetics were not different when their concentrations were corrected for minimum alveolar anesthetic concentration values. Bay K 8644 significantly prevented the anesthetic-depressed amplitude (P < 0.05). We conclude that sevoflurane, isoflurane, and halothane have direct myocardial depressant effects on cultured neonatal rat ventricular myocytes and that the reduction of sarcolemmal L-type Ca2+ channel current levels mediates the myocardial depression observed in these immature hearts. IMPLICATIONS: Sevoflurane, isoflurane, and halothane have a direct cardiodepressant effect on cardiac excitation-contraction coupling in the immature heart, which is mediated by an interaction with the L-type Ca2+ channel.

Role of nitric oxide production through M2-cholinergic receptors in cultured rat ventricular myocytes.

We previously reported that carbachol (CCh) caused the enhancement of NO production coinciding with negative chronotropy in cultured rat ventricular myocytes. In this study, we examined which subtype of muscarinic cholinergic receptor mediated these effects of CCh by measuring the NOx production with an HPLC-Griess reaction system and monitoring the beating with a Fotonic Sensor. The enhancement of NO production and negative chronotropy by 10(-4) M CCh stimulation were significantly inhibited by 10(-6) M atropine, 10(-6) M methoctramine, 3 x 10(-4) M L-NMMA, and 10(-5) M methylene blue. On the other hand, 10(-6) M pirenzepine and 10(-6) M HHSiD had no influence on the negative chronotropy by 10(-4) M CCh stimulation. Both 10(-6) M pirenzepine and 10(-6) M HHSiD suppressed the enhancement of NO production by 10(-4) M CCh stimulation slightly though not statistically. In addition, the m2 cholinergic receptor gene was expressed in our cell preparations, as demonstrated by reverse-transcriptase/PCR analysis. We concluded that M2-cholinergic receptor-mediated negative chronotropy may be due in part to activation of the NO-signaling pathway in cultured rat ventricular myocytes.

Ruthenium red inhibits cytosolic Ca2+ oscillations induced by vasopressin in primary cultured hepatocytes.

The effects of ruthenium red were investigated on the vasopressin (Vp)-induced Ca2+ response in single, primary cultured rat hepatocytes loaded with fura-2. Low concentrations of Vp (1 nM) evoked a sustained train of baseline spike Ca2+ oscillations, with a latency to first peak of 170 s and a frequency of 0.37 min(-1). Treatment of hepatocytes with a higher concentration of Vp (10 nM) resulted in a rapid rise in intracellular Ca2+, with less delay (40 s), and which remained elevated and sustained. Microinjection of a low concentration of ruthenium red (10 microM in the injection pipette) altered the observed response to 1 nM Vp such that only 2 - 4 base line spikes were observed. A higher concentration of ruthenium red (50 microM in the injection pipette) completely abolished the 1 nM Vp response. However, the Ca2+ responses to higher concentrations of Vp (10 nM) or to the Ca2+-ATPase inhibitor, thapsigargin, were unaffected by ruthenium red. These results show that low concentrations of ruthenium red inhibit the Vp-induced oscillatory Ca2+ response and suggest a contribution of a ryanodine receptor-mediated Ca2+-induced Ca2+ release in generating the baseline spike oscillations in rat hepatocytes.

Relation between spontaneous contraction and sarcoplasmic reticulum function in cultured neonatal rat cardiac myocytes.

The relation between spontaneous contraction, Ca2+ oscillations, and sarcoplasmic reticulum (SR) function was studied in cultured neonatal rat cardiac myocytes. Spontaneous contraction and Ca2+ oscillations were irregular at day 2 of culture but became regular at day 6 of culture in neonatal rat cardiac myocytes. The rate of spontaneous contraction and the frequency of Ca2+ oscillations were decreased by verapamil and were abolished in the absence of extracellular Ca2+ at both day 2 and day 6 of culture. Ryanodine and thapsigargin increased the rate of contraction and the frequency of Ca2+ oscillations at day 2 of culture but did not affect contractions and Ca2+ oscillations at day 6 of culture. Ultrastructural observation showed that the structure of SR developed less at day 6 of culture. The present results suggest that spontaneous contraction and Ca2+ oscillations are due mainly to extracellular Ca2+ influx but not to Ca2+ release from SR in neonatal rat cardiac myocytes.

Ca2+ channel modulation alters halothane-induced depression of ventricular myocytes.

PURPOSE: This study examined the direct myocardial depressant effect of halothane and determined whether an L-type Ca2+ channel agonist and antagonists altered the myocardial depression induced by halothane in cultured rat ventricular myocytes. METHODS: Ventricular myocytes were obtained from neonatal rats by enzymatic digestion with collagenase and then cultured for 6 to 7 days. The myocytes were stabilized in a serum-free medium, and the spontaneous beating rate and amplitude were measured. To assess the halothane-induced conformational changes in L-type Ca2+ channel, receptor binding study was performed using a dihydropyridine derivative, [3H] PN 200-110, in cardiac membrane preparation. RESULTS: Halothane (1%, 2%, 3%, 4%) decreased the beating rate and amplitude in a concentration-dependent manner (P < 0.05). The myocardial depressant effects of halothane were potentiated by nifedipine or verapamil (P < 0.05). Bay K 8644, an L-type Ca2+ channel agonist, completely prevented the halothane-induced depression in amplitude (P < 0.05), but affected the beating rate less. Adding halothane (2%) decreased (P < 0.05) the maximum binding site density for [3H] PN 200-110 (from 198.6 +/- 23.7 fmol.mg-1 protein to 115.3 +/- 21.6 fmol.mg-1 protein) but did not affect binding affinity (from 0.461 +/- 0.077 nM to 0.307 +/- 0.055 nM). CONCLUSION: The reduction of Ca2+ current via sarcolemmal L-type Ca2+ channel, probably due to conformational changes in dihydropyridine binding sites, plays an important role in halothane-induced myocardial depression in living heart cells.

Molecular diversity and double regulatory mechanism of activation of phospholipase C in rat brain.

Whereas evidence for a G protein-dependent stimulation of phospholipase C (PLC) is abundant, reports on the inhibition of PLC through a G protein-mediated pathway have only recently begun to appear. In the present study, cerebral cortex membranes were chosen since they have a readily measurable Gpp[NH]p and Ca2+-stimulated PLC activity. Nanomolar concentrations of Gpp[NH]p, a hydrolysis-resistant GTP analogue, inhibited basal inositol 1,4,5-trisphosphate (IP3) production, with a maximum inhibition of 25% at 10 nM. Increasing the concentrations of Gpp[NH]p to over 10 nM resulted in a reversal of the inhibitory effect and onset of stimulation of IP3 production. GDPbetaS as a G protein inhibitor and U-73122 as a putative PLC-beta inhibitor had little effect on basal IP3 production at 100 microM and 1 microM, respectively. However, GDPbetaS and U-73122 completely antagonized both the inhibition and the stimulation of IP3 production produced by lower and higher concentrations, respectively, of Gpp[NH]p. Rat cortical membranes expressed a greater amount of PLC-beta1. These data suggest that PLC-beta1 isozymes may be regulated by both inhibitory and stimulatory G protein-mediated mechanisms.

Alteration in Ca2+/calmodulin-sensitive adenylyl cyclase activity in the hippocampus of stroke-prone spontaneously hypertensive rats.

This study examined the function of adenylyl cyclase (AC) activity in the hippocampus and cerebral cortex of the stroke-prone spontaneously hypertensive rat (SHRSP). Male SHRSP (8-week-old and 25-week-old) were used for the experiments, and age-matched Wistar-Kyoto rats (WKY) were used as a genetic control. Basal, forskolin-, and GppNHp-stimulated AC activities were not different between SHRSP and WKY in the 8-week-old and 25-week-old groups. Ca2+/calmodulin-sensitive AC activity in hippocampal and cerebral cortex membranes was significantly lower in 25-week-old SHRSP than in age-matched WKY, but it was not in the 8-week-old group. These results suggest that the function of Ca2+/calmodulin-sensitive, presumably type I, AC was impaired in the brain of SHRSP. Such dysfunction of AC possibly contributes to the behavioral impairment reported in passive avoidance tasks in SHRSP.

Inhibitory effects of tyrosine kinase inhibitors on capacitative Ca2+ entry in rat glioma C6 cells.

The effects of genistein and erbstatin analogue, inhibitors of tyrosine kinase, on Ca2+ mobilization evoked by thapsigargin (TG) were examined in rat glioma C6 cells. Genistein and erbstatin analogue inhibited the Ca2+ release from intracellular pools as well as Ca2+ entry from extracellular medium evoked by TG in a dose-dependent manner. However, they did not affect a Ca2+ entry due to leakage of Ca2+ from extracellular medium into cells. The present results suggest that tyrosine kinase inhibitors inhibit capacitative Ca2+ entry due to the inhibition of both Ca2+ entry itself and Ca2+ release in rat glioma C6 cells.