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


CONCLUSIONS
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.
Department of Physiology, Huazhong University of Science and Technology, Wuhan, China.
An-tao
AT
Luo
Hong-yan
HY
Luo
Xin-wu
XW
Hu
Lin-lin
LL
Gao
Hua-min
HM
Liang
Ming
M
Tang
Jürgen
J
Hescheler
D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism / Q000502:physiology*; D018929:Cell Culture Techniques; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D005260:Female; D006352:Heart Ventricles / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects*; D007545:Isoproterenol / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D011493:Protein Kinase C / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction
D020746:Calcium Channels, L-Type; D047428:Protein Kinase Inhibitors; D005576:Colforsin; D017868:Cyclic AMP-Dependent Protein Kinases; D017869:Cyclic GMP-Dependent Protein Kinases; D011493:Protein Kinase C; D007545:Isoproterenol