Protein kinase C-mediated up-regulation of Na+/Ca2+-exchanger in rat hepatocytes determined by a new Na+/Ca2+-exchanger inhibitor, KB-R7943.
The regulatory mechanism of the plasma membrane Na+/Ca2+-exchanger in isolated rat hepatocytes was studied using microspectrofluorometry and 45Ca2+ uptake methods. Exposure of single hepatocytes to low-Na+ solutions induced an increase in the intracellular Ca2+ concentration ([Ca2+]i) which depended on the presence of extracellular Ca2+. 2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea methanesulfonate (KB-R7943), a novel selective inhibitor of Na+/Ca2+-exchangers, inhibited the initial rate of [Ca2+]i increase induced by exposure to the low-Na+ solution (IC50 = 2 microM). KB-R7943 also reduced the initial rate of 45Ca2+ uptake (IC50 = 4 microM). The increase in [Ca2+]i induced by exposure to the low-Na+ solution was inhibited by pre-incubation with 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7, 50 microM), but not with N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide (H-8, 60 microM) or a tyrosine kinase inhibitor, genistein (100 microM). Furthermore, taurocholate and phorbol-12,13-dibutyrate, both of which activate protein kinase C, promoted the increase in [Ca2+]i. These [Ca2+]i increases were sensitive to KB-R7943. Our results indicate that the Na+/Ca2+-exchanger is up-regulated via protein kinase C. The activity of Na+/Ca2+-exchangers is not evident under normal physiological conditions, suggesting that the exchanger may be activated under pathophysiological conditions.
Ikari
A
A
Department of Pharmaceutical Physiology, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Japan. g4720203@ms.toyama-mpu.ac.jp
Sakai
H
H
Takeguchi
N
N
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000493:pharmacokinetics; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D005110:Extracellular Space / Q000737:chemistry / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects*; D008297:Male; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology; D015854:Up-Regulation; D014700:Verapamil / Q000494:pharmacology
C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D002121:Calcium Channel Blockers; D019831:Sodium-Calcium Exchanger; D012964:Sodium; D014700:Verapamil; D011493:Protein Kinase C; D004110:Diltiazem; D013890:Thiourea; D002118:Calcium