Mechanism of gamete shedding in starfish: Involvement of acetylcholine in extracellular Ca2+-dependent contraction of gonadal walls.

Starfish are suitable animals for the study of hormonal regulatory mechanism of oocyte maturation and ovulation. Although contraction of the gonadal walls is essential for the shedding gametes, little was known about the mechanism. When ovaries of starfish Patiria pectinifera were incubated in Ca2+-free seawater in the presence of 1-methyladenine (1-MeAde), the germinal vesicles in oocytes broke down, but no ovulation occurred. Verapamil, a potent inhibitor of voltage-dependent Ca2+ channels, inhibited 1-MeAde-induced ovulation. These results suggest that extracellular Ca2+ and its influx are indispensable for gamete shedding. Furthermore, acetylcholine (ACh) was involved in extracellular Ca2+-dependent contractions of gonadal walls. Although 1-MeAde failed to induce contraction of the gonadal walls in normal seawater containing L-glutamic acid, application of ACh or carbachol, an agonist for ACh receptor, could bring about shedding of mature oocytes. Atropine, a competitive antagonist of the muscarinic ACh receptor, inhibited 1-MeAde-induced ovulation, but a nicotinic ACh receptor antagonist mecamylamine had no effect. Furthermore, ACh was detected in the ovaries and testes in P. pectinifera. These findings suggest that ACh acts on muscarinic ACh receptors in gonadal walls to induce peristaltic contractions caused by Ca2+ influx via Ca2+ channels in the gonadal wall muscle for gamete shedding. The present study also provides new insight into the regulatory mechanism that 1-MeAde acts on secretion of ACh in ovaries and testes.

Effect of subarachnoid hemorrhage on voltage-dependence calcium channel current in cerebral artery smooth muscle cells.

OBJECTIVE: To investigate the effect of subarachnoid hemorrhage (SAH) on voltage-dependent calcium channel (VDCC) current in cerebral artery smooth muscle cells (SMCs), oxyhemoglobins (OxyHb) concentration and vasospasm. METHOD: Thirty-six clean SD rats were used to establish SAH model by injecting autologous arterial blood into suprasellar cistern with the aid of stereotaxic instrument. They were divided into arterial SAH group (14 rats), venous SAH group (13 rats) and sham operation group (9 rats), and OxyHb concentrations were measured in the first two groups. Relative membrane surface area of cerebral artery SMCs, resting potential and VDCC current were measured using a patch clamp at day 3 after modeling; cerebral blood flow (CBF) was measured by using fluorescent microsphere-based lateral flow assay. RESULTS: OxyHb concentration of arterial SAH group (127±4 g/L) was higher than that of venous SAH group (54±6 g/L) and sham operation group (50±5 g/L), with significant difference (P<0.05); The maximum VDCC current (3.22±0.31 pA/pF) of the arterial SAH group was obviously higher than that of venous SAH group (2.19±0.27 pA/pF) and sham operation group (2.18±0.29 pA/pF), also showing a significant difference (P<0.05). For arterial SAH group, VDCC current consisted of L- and R-type calcium current, and for venous SAH group the VDCC current consisted of L-type calcium current; CBF of arterial SAH group (0.83±0.14 ml/g/min) was significantly higher than that of venous SAH group (1.28±0.28 ml/g/min) and sham operation group (1.35±0.19 ml/g/min) (P<0.05). CONCLUSION: The effect of arterial SAH was greater on the expression and function of VDCCs in cerebral artery SMCs than venous SAH. This may be explained by the differences in the concentration and composition of pathogenic agents for vasospasm in the arterial and venous blood, such as OxyHb.

Voltage-dependent Calcium Channel (VDCC) alpha(1A) Subunit Expression in the Ataxic Mutant, Pogo Mice Cerebellum / 대한해부학회지

The pogo mouse is a new ataxic mutant derived from a Korean wild mouse. The pogo mutation is inherited as an autosomal recessive trait on chromosome 8. Mutations in gene coding for the alpha(1A)subunit of voltagegated P/Q-type Ca(2+) channel have been shown to cause phenotypes in humans and mice, i.e., tottering, leaner, rolling mouse mouse Nagoya. Using immunohistochemistry, the expression of the alpha(1A)subunit of voltage-gated P/Q-type Ca(2+) channel was examined in pogo mice cerebellum including deep cerebellar nuclei (DCN). We observed alpha(1A)immunoreactivity in the cerebellar cortex (Purkinje cell and granule cell) and DCN of ataxic pogo mice and heterozygote control mice. There was no difference in cerebellar cortical alpha(1A)immunoreactivity between ataxic pogo mice and heterozygous littermate controls (pogo/+). However, we observed alpha(1A)immunoreactivity in the Purkinje cells of control and ataxic pogo mice cerebellum and DCN. We found a significant difference between pogo and heterozygous controls in terms of alpha(1A)immunoreactivities in the DCN. alpha(1A)immunoreactivity in this nucleus in pogo was much higher than in heterozygous littermate controls. No significant differences were observed in the interposed nucleus between pogo and heterozygous controls, but we found that the alpha(1A)subunits were clearer and more abundant in the lateral and medial regions of pogo than in control mice in these regions, where only weak immunoreactivity was observed. This elevated expression of the alpha(1A)subunit in deep cerebellar neurons of pogo might be a compensation for the altered function of P/Q type calcium channel and be related with the induction of the ataxic phenotype in pogo mice.