Role of calcium stores and membrane voltage in the generation of slow wave action potentials in guinea-pig gastric pylorus.

1. Intracellular recordings made in single bundle strips of a visceral smooth muscle revealed rhythmic spontaneous membrane depolarizations termed slow waves (SWs). These exhibited 'pacemaker' and 'regenerative' components composed of summations of more elementary events termed spontaneous transient depolarizations (STDs). 2. STDs and SWs persisted in the presence of tetrodotoxin, nifedipine and ryanodine, and upon brief exposure to Ca2+-free Cd2+-containing solutions; they were enhanced by ACh and blocked by BAPTA AM, cyclopiazonic acid and caffeine. 3. SWs were also inhibited in heparin-loaded strips. SWs were observed over a wide range of membrane potentials (e.g. -80 to -45 mV) with increased frequencies at more depolarized potentials. 4. Regular spontaneous SW activity in this preparation began after 1-3 h superfusion of the tissue with physiological saline following the dissection procedure. Membrane depolarization applied before the onset of this activity induced bursts of STD-like events (termed the 'initial' response) which, when larger than threshold levels initiated regenerative responses. The combined initial-regenerative waveform was termed the SW-like action potential. 5. Voltage-induced responses exhibited large variable latencies (typical range 0.3-4 s), refractory periods of approximately 11 s and a pharmacology that was indistinguishable from those of STDs and spontaneous SWs. 6. The data indicate that SWs arise through more elementary inositol 1,4,5-trisphosphate (IP3) receptor-induced Ca2+ release events which rhythmically synchronize to trigger regenerative Ca2+ release and induce inward current across the plasmalemma. The finding that action potentials, which were indistinguishable from SWs, could be evoked by depolarization suggests that membrane potential modulates IP3 production. Voltage feedback on intracellular IP3-sensitive Ca2+ release is likely to have a major influence on the generation and propagation of SWs.

Prevention of high blood pressure by reducing sympathetic innervation in the spontaneously hypertensive rat.

It has previously been reported that the increase in blood pressure in the spontaneously hypertensive rat (SHR) occurs concurrently with a marked increase in thickness of the arterial wall and an increase in vascular innervation, particularly for the small muscular arteries. The purpose of the present study was to determine whether prevention of the increase in vascular innervation could prevent elevation of blood pressure in the SHR. We found that intraperitoneal injection of a single dose of an antiserum to nerve growth factor (anti-NGF) into young SHRs (postnatal day 19-24) caused a marked reduction in mean blood pressure at age 3-4 months from the raised value of 24.2 +/- 0.5 kPa to 18.9 +/- 0.8 kPa. By comparison, treated Wistar Kyoto rats (WKYs) maintained normal blood pressures. The treatment reduced the amplitude of the intracellularly recorded excitatory junction potential and the NA content of mesenteric arteries in the SHR, leaving the values similar to those of control WKYs. The NA content of these vessels was also reduced in treated WKYs. Importantly, the thickness of the vessel wall, which was greater in the SHR than the WKY, was not significantly altered by anti-NGF treatment. It is concluded that anti-NGF treatment during late neonatal development inhibits the increase in the functional levels of vascular innervation observed in the SHR. Furthermore, this increase in the functional levels of vascular innervation is necessary for the development of hypertension in this rat strain.

Effects of catecholamines and diazepam in chloroquine poisoning in barbiturate anaesthetised rats.

The recommended treatment of human chloroquine poisoning is diazepam and adrenaline but neither has been evaluated in controlled clinical trials. We investigated whether diazepam provided any added benefit over barbiturate anaesthesia and whether the protective effect of catecholamines in chloroquine poisoning was mediated through alpha or beta receptor stimulation. Rats, anaesthetised with thiobutobarbitone had a continuous intravenous infusion of 3 mg/kg/min of chloroquine. This caused a steady decline in pulse rate and blood pressure. When diazepam (3 mg/kg iv) was administered 5-10 min later, heart rates decreased at a faster rate (P = 0.005), blood pressure was consistently lower (P = 0.01) and there was a shorter time to arrhythmias and death (P < 0.05). Adrenergic agents were given by titration to attempt to maintain mean blood pressure > 75 mmHg. Compared with the phenylephrine (selective alpha agonist) group, the group treated with isoprenaline (selective beta agonist) had faster heart rates which decreased more slowly (P < 0.0001), higher blood pressure (P = 0.005) and longer time to arrhythmias and death (P = 0.005). Adrenaline and noradrenaline had intermediate effects. Thus beta agonist effect appears to explain the beneficial effects of adrenaline but alpha agonist activity may be harmful. This animal work suggests that a combination of barbiturate anaesthesia and isoprenaline may be better than the diazepam and adrenaline in combatting the effects of chloroquine.

The sigma receptor ligand, reduced haloperidol, induces apoptosis and increases intracellular-free calcium levels [Ca2+]i in colon and mammary adenocarcinoma cells.

The sigma receptor ligand reduced haloperidol (50 and 100 microM), potently inhibited cell proliferation, and induced apoptosis in WIDr colon and MCF-7 adenocarcinoma cell lines. Apoptosis was confirmed after drug treatment of the cells by the presence of nuclear fragmentation after staining of the cells with Hoechst 33258 and cellular DNA fragmentation ELISA and by condensation of the heterochromatin using transmission electron microscopy. However, internucleosomal DNA cleavage was not detected using gel electrophoresis. Reduced haloperidol (100 microM) increased the intracellular free calcium levels [Ca2+]i in both cell lines, which was independent of extracellular calcium, suggesting that the rise in [Ca2+]i was from intracellular stores and that an increase in [Ca2+]i may act as a "trigger" for apoptosis in these cell lines.

WEB-2086 and indomethacin do not modify blood pressure fall on unclipping hypertensive rats.

1. Pretreatment with intravenous WEB-2086 (0.5 mg/kg; an antagonist of the actions of platelet activating factor; PAF) with or without indomethacin (2 mg/kg) failed to prevent or modify the fall in blood pressure following unclipping of the renal artery of anaesthetized two-kidney, one-clip hypertensive rats. 2. The same medications given to two other groups of rats 60 min after unclipping when the blood pressure had fallen to stable levels failed to reverse the fall. 3. Despite evidence that both prostanoids and PAF can be detected in increased amounts in renal venous blood after unclipping, they do not appear to mediate the reduction in blood pressure in this model of reversible hypertension.

Endothelium-dependent inhibition of sympathetic vasoconstriction by frusemide administration to rats.

1. Segments of the tail artery of the rat were cannulated at both ends and mounted in an organ bath filled with Krebs solution. 2. Using an extracorporeal circuit, blood was pumped at a constant 2 ml/min from the carotid artery of anaesthetized rats to perfuse the segment of tail artery and returned to the donor rat via the jugular vein. 3. Peri-arterial electrical stimulation of the ex vivo blood perfused tail artery at 5 Hz produced vasoconstriction and an increase in perfusion pressure. 4. The intravenous administration of frusemide 5 mg/kg to the donor rat resulted in an inhibition of the vasoconstrictor responses of the perfused tail artery segment. Diuresis-induced losses of volume and frusemide were prevented by a urinary bladder-venous shunt. 5. Removal of the endothelium from the tail artery segment, by perfusion with dry gas for 4 min, prevented the vasoconstrictor-inhibitory effect of frusemide administration. Removal of the endothelium was confirmed histologically and by the absence of a vasodilator response to acetylcholine. 6. On the basis of these and previous results it is concluded that parenteral frusemide administration releases an unidentified but non-prostanoid hormone from the kidney which produces an endothelium-dependent inhibition of sympathetic vasoconstriction.

Omeprazole: effects on oxidative drug metabolism in the rat.

Omeprazole, a substituted benzimidazole and a potent gastric antisecretory drug has been tested for inhibition of microsomal drug oxidative function in the rat. A single dose of 40 mg/kg prolonged pentobarbitone sleeping times from 118 (range 73-168) min to 195 (159-222) min (P less than 0.01), pentobarbitone half-lives from 89 (63-114) to 112 (54-146) min (P less than 0.05) and aminopyrine breath 14CO2 half-lives from 43 (37-51) to 56 (49-79) min (P less than 0.05). Omeprazole in doses of 20 mg/kg or less had no significant effect. In prolonging pentobarbitone sleeping times omeprazole 40 mg/kg and an equimolar (30 mg/kg) dose of cimetidine were approximately equipotent. These results contrast with studies in man in which much smaller doses of omeprazole have been shown to produce clinically significant inhibition of drug metabolism.

The effect of salt intake on cyclosporine-induced impairment of renal function in rats.

Three groups of rats were fed a low-sodium diet. Groups 1 drank water and was treated with cyclosporine, 100 mg kg-1 48 h-1 p.o. for 3 weeks (low-salt-treated group). Group 2 drank 0.15 M saline and was also treated with cyclosporine (high-salt-treated group). Group 3 drank water and was treated with the vehicle (low-salt-vehicle group). Measurements were made during a control period and weekly during the 3-week treatment period and a 3-week recovery period. Both cyclosporine-treated groups lost weight during treatment but the rises in serum creatinine and blood urea and decrease in creatinine clearance were greater in the low-salt group. The vehicle group gained weight and had no change in the other parameters over the three weeks. There was an increase in urine volume and sodium excretion in the high-salt group associated with cyclosporine treatment. Although the low-salt groups had a higher plasma renin concentration than the high-salt group there were no changes produced by cyclosporine treatment. Histopathological examination showed mild tubular lesions with vacuolar degeneration of proximal tubular cells. This was more prevalent in the low-salt-cyclosporine-treated group. The plasma concentrations of cyclosporine were not different after one-week treatment but were slightly greater after 2 week and 3-week treatment in the low-salt group. We have suggested that the greater impairment of renal function in the low-salt group produced by cyclosporine may be contributed to by an involvement of tubuloglomerular feedback.