Effects of reduced external sodium concentration and multivalent cations on caffeine contractures in young ferret atrial trabeculae.
The characteristics of caffeine (1.25-80 mM) transient contractures have been examined in small atrial trabeculae (diameters 50-250 microns) isolated from young (1-1.5 months) ferret hearts. In the control medium, the half-saturation constant and the maximum contracture strength (at infinite caffeine concentration) were 37.8 +/- 10.2 mM and 0.9 +/- 0.2 kN.kg-1 (n = 11), respectively. The contractile response to caffeine was markedly enhanced following reduction of external sodium (70-0 mM). The perfusion of young ferret trabeculae with the sodium-free medium (up to 3 min) decreased the half-saturation constant by a factor of three (12.4 +/- 1.6 mM, n = 8) with an increase in maximum contracture strength (1.09 +/- 0.3 kN.kg-1, n = 8). The effects of various divalent and trivalent cations have been tested on the 10 mM caffeine contracture in trabeculae perfused with Na-containing (140 mM) solution. The order of cation effectiveness is Gd3+ (half effect 0.04-0.07 mM) greater than Cd2+ (0.15-0.25 mM) greater than Ni2+ (2-2.5 mM) greater than Co2+ (7-7.5 mM) much greater than Mn2+. In conclusion, the present work has shown that in atrial trabeculae isolated from young ferret hearts, the strength of the caffeine contracture was markedly affected by the activity of the sarcolemmal Na-Ca exchange.
Noireaud
J
J
Laboratory of General Physiology, National Veterinary School, University of Nantes, France.
Baudet
S
S
Huchet
C
C
Leoty
C
C
D000818:Animals; D016275:Atrial Function; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002412:Cations / Q000494:pharmacology; D005289:Ferrets; D006325:Heart Atria / Q000187:drug effects; D066298:In Vitro Techniques; D007474:Ion Exchange; D009200:Myocardial Contraction / Q000187:drug effects* / Q000502:physiology; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology
D002412:Cations; D002110:Caffeine; D012964:Sodium; D002118:Calcium