Hyposmotic challenge modulates function of L-type calcium channel in rat ventricular myocytes through protein kinase C

Aim: To study the effects and mechanisms by which hyposmotic challenge modulate function of L-type calcium current (I-Ca,I-L) in rat ventricular myocytes. Methods: The whole-cell patch-clamp techniques were used to record I-Ca,I-L in rat ventricular myocytes. Results: Hyposmotic challenge(similar to 220 mosmol/L) induced biphasic changes of I-Ca,I-L, a transient increase followed by a sustained decrease. I-Ca,I-L increased by 19.1%+/- 6.1% after short exposure (within 3 min) to hyposmotic solution. On the contrary, long hyposmotic challenge (10 min) decreased I-Ca,I-L to 78.1%+/- 11.0% of control, caused the inactivation of I-Ca,I-L, and shifted the steady-state inactivation curve of I-Ca,I-L to the right. The decreased I-Ca,I-L induced by hyposmotic swelling was reversed by isoproterenol or protein kinase A (PKA) activator foskolin. Hyposmotic swelling also reduced the stimulated I-Ca,I-L by isoproterenol or foskolin. PKA inhibitor H-89 abolished swelling-induced transient increase of I-Ca,I-L, but did not affect the swelling-induced sustained decrease of I-Ca,I-L. NO donor SNAP and protein kinase G (PKG) inhibitor Rp-8-Br-PET-cGMPS did not interfere with swelling-induced biphasic changes of I-Ca,I-L. Protein kinase C (PKC) activator PMA decreased I-Ca,I-L and hyposmotic solution with PMA reverted the decreased I-Ca,I-L by PMA. PKC inhibitor BIM prevented the swelling-induced biphasic changes of I-Ca,I-L. Conclusion: Hyposmotic challenge induced biphasic changes of I-Ca,I-L, a transient increase followed by a sustained decrease, in rat ventricular myocytes through PKC pathway, but not PKG pathway. PKA system could be responsible for the transient increase of I-Ca,I-L during short exposure to hyposmotic solution