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