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

To study the effects and mechanisms by which hyposmotic challenge modulate function of L-type calcium current (I(Ca,L)) in rat ventricular myocytes.

The whole-cell patch-clamp techniques were used to record I(Ca,L) in rat ventricular myocytes.

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).

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.