Chronic verapamil treatment remodels ICa,L in mouse ventricle.
In this study we tested the hypothesis that ventricular homeostasis of L-type Ca(2+) current (I(Ca,L)) minimally involves regulation of the main pore-forming alpha-subunit (Ca(V)1.2) and auxiliary proteins that serve as positive or negative regulators of I(Ca,L). We treated animals for 24 h with verapamil (Ver, 3.6 mg.kg(-1).day(-1)), isoproterenol (Iso, 30 mg.kg(-1).day(-1)), or Iso + Ver via osmotic minipumps. To test for alterations of Ca(2+) channel complex components we performed real-time PCR and Western blot analysis on ventricle. In addition, cardiac myocytes (CMs) were dispersed and current was recorded in the whole cell configuration to evaluate I(Ca,L). Surprisingly, 24- to 48-h Ver increased Ca(V)1.2 mRNA and protein and I(Ca,L) current (Ver 11 +/- 1pA/pF vs. control 7 +/- 0.5pA/pF; P < 0.01). I(Ca,L) from CMs in Ver mice showed no change in whole cell capacitance. To examine the in vivo effects of a physiologically relevant Ca(2+) channel agonist, we treated mice with Iso. Twenty-four-hour Iso infusion increased heart rate; Ca(V)1.2- and Ca(V)beta(2) mRNA levels were constant, but the Ca(2+) channel subunit mRNA Rem was increased twofold. Cells isolated from 24-h Iso hearts showed no change in basal I(Ca,L) density and diminished responsiveness to acute 1 muM Iso. To further examine the homeostatic regulation of the Ca(2+) channel, we treated animals for 24 h with Iso + Ver. The influence of Iso + Ver was similar that of to Iso alone on Ca(2+) channel mRNAs and I(Ca,L), with the exception that it prevented the increase in Rem seen with Iso treatment. Long-term Ca(2+) channel blockade induces an increase of Ca(V)1.2 mRNA and protein and significantly increases I(Ca,L).
Schroder
Elizabeth
E
Department of Physiology, University of Kentucky, Lexington, Kentucky 40536-0298, USA. eschr0@uky.edu
Magyar
Janos
J
Burgess
Don
D
Andres
Douglas
D
Satin
Jonathan
J
D000200:Action Potentials / Q000187:drug effects; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000235:genetics* / Q000378:metabolism; D004562:Electrocardiography; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D032383:Myocytes, Cardiac / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology*
D000318:Adrenergic beta-Agonists; C514350:CACNA1C protein, mouse; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D012333:RNA, Messenger; D014700:Verapamil; D007545:Isoproterenol