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,L) in rat ventricular myocytes.

Methods:

The whole-cell patch-clamp techniques were used to record I_Ca,L in rat ventricular myocytes.

Results:

Hyposmotic challenge(～220 mosmol/L) induced biphasic changes of I_Ca,L, a transient increase followed by a sustained decrease. I_Ca,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,L to 78.1%±11.0% of control, caused the inactivation of I_Ca,L, and shifted the steady-state inactivation curve of I_Ca,L to the right. The decreased I_Ca,L induced by hyposmotic swelling was reversed by isoproterenol or protein kinase A (PKA) activator foskolin. Hyposmotic swelling also reduced the stimulated I_Ca,L by isoproterenol or foskolin. PKA inhibitor H-89 abolished swelling-induced transient increase of I_Ca,L, but did not affect the swelling-induced sustained decrease of I_Ca,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,L. Protein kinase C (PKC) activator PMA decreased I_Ca,L and hyposmotic solution with PMA reverted the decreased I_Ca,L by PMA. PKC inhibitor BIM prevented the swelling-induced biphasic changes of I_Ca,L.

Conclusion:

Hyposmotic challenge induced biphasic changes of I_Ca,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,L during short exposure to hyposmotic solution.