Effects of bivalent cations on post-rest adaptation in guinea-pig heart muscle.
In isolated papillary muscles of guinea-pig hearts, the inotropic effects of bivalent cations, Ca2+, Ba2+, Sr2+, and Ni2+, were investigated during post-rest adaptation in order to study their individual action on excitation-contraction coupling. Upon exposure to each cation studied, the force of contraction was transiently enhanced, whereas the steady state force was influenced differently: it increased with Ca2+, Ba2+ and Sr2+ and was depressed by Ni2+. The transmembrane action potentials (measured at 90% repolarization) were slightly prolonged by Sr2+ and even more by Ba2+, and were shortened by Ca2+ and Ni2+. After 10 min rest, the post-rest contractions consisted of a late peak (PII) that was enhanced in high Ca2+-solution an by Sr2+. Ni2+ and Ba2+ depressed PII and during adaptation to pre-rest controls an early peak of contraction (PI) prevailed. There was no simple relation between post-rest adaptation of force and the duration of action potential in the presence of the bivalent cations tested. During post-rest adaptation the two components of contraction can be separated. The results are interpreted in terms of a model of excitation-contraction coupling which derives Ca ions for contractile activation from two sources: transmembrane calcium influx and calcium release from cellular stores. From the different effects on post-rest adaptation it is concluded that the individual cations influence excitation-contraction coupling more specifically and not merely by "screening-off" the negative surface charges.
Beyer
T
T
Institut für Pharmakologie der Universität Kiel, FRG.
Hergeröder
W
W
Ravens
U
U
D000200:Action Potentials / Q000187:drug effects; D000222:Adaptation, Physiological; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects*; D009532:Nickel / Q000494:pharmacology; D010210:Papillary Muscles / Q000187:drug effects* / Q000502:physiology; D012146:Rest; D013324:Strontium / Q000494:pharmacology
D002413:Cations, Divalent; D001464:Barium; D009532:Nickel; D002118:Calcium; D013324:Strontium