B-type natriuretic peptide (BNP) attenuates the L-type calcium current and regulates ventricular myocyte function.
A fundamental question in physiology is how hormones regulate the functioning of a cell or organ. It was therefore the aim of this study to investigate the effect(s) of BNP-32 on calcium handling by ventricular myocytes obtained from the rat left ventricle. We specifically tested the hypothesis that BNP-32 decreased the L-type calcium current (I(Ca,L)). Perforated patch clamp technique was used to record I(Ca,L) and action potential (AP) in voltage and current clamp mode, respectively. Myocyte shortening was measured using a photodiode array edge-detection system and intracellular calcium transients were measured by fluorescence photometry. Western blotting was used to determine the relative change in the expression of proteins. At the concentrations tested, BNP-32 significantly decreased cell shortening in a dose-dependent manner; increased the phase II slope of the AP by 53.0%; increased the APD(50) by 16.9%; reduced the I(Ca,L) amplitude with a 22.9% decrease in the peak amplitude and reduced Ca(2+)-dependent inactivation; increased the V(1/2) activation of the L-type calcium channel by 51.1% and decreased V(1/2) inactivation by 31.8%; and, intracellular calcium transient amplitude was significantly decreased by 32.0%, whereas the time to peak amplitude and T(1/2) were both significantly increased by 38.7% and 89.4% respectively. Sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a) protein expression was reduced by BNP-32. These data suggest that BNP-32 regulates ventricular myocyte function by attenuating I(Ca,L), altering the AP and reducing SERCA2a activity and/or expression. This study suggests a novel constitutive mechanism for the autocrine action of BNP on the L-type calcium channel in ventricular myocytes.
Sodi
R
R
Department of Clinical Biochemistry & Metabolic Medicine, Royal Liverpool & Broadgreen University Hospital, Prescot street, Liverpool L7 8XP, United Kingdom. ravsodi@yahoo.com
Dubuis
E
E
Shenkin
A
A
Hart
G
G
D000818:Animals; D020746:Calcium Channels, L-Type / Q000187:drug effects* / Q000378:metabolism*; D004594:Electrophysiology; D066298:In Vitro Techniques; D008297:Male; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000502:physiology*; D020097:Natriuretic Peptide, Brain / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism
D020746:Calcium Channels, L-Type; D020097:Natriuretic Peptide, Brain; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases