Effects of caffeine on potassium currents in isolated rat ventricular myocytes.
Rapid exposure of cardiac muscle to high concentrations of caffeine releases Ca(2+) from the sarcoplasmic reticulum (SR). This Ca(2+) is then extruded from the cell by the Na(+)/Ca(2+) exchanger. Measurement of the current carried by the exchanger (I(Na/Ca)) can therefore be used to estimate of the Ca(2+) content of the SR. Previous studies have shown that caffeine, however, can also inhibit K(+) currents. We therefore investigated whether the inhibitory effects of caffeine on these currents could contaminate measurements of I(Na/Ca). Caffeine caused partial inhibition of the inward rectifier K(+) current (I(K1)): the outward current at -40 mV was 1.15+/-0.24 pA/pF in control and decreased to 0.34+/-0.15 pA/pF in the presence of 10 mmol/l caffeine (P<0.05, n=15). This was similar to the effect of caffeine on the holding current observed at -40 mV in the absence of K(+) channel block and could therefore account for the contaminating effects of caffeine observed during measurements of I(Na/Ca). Moreover, caffeine also partially inhibited the transient outward ( I(to)) and the delayed rectifier (I(K)) K(+) currents.
Department of Medicine, University Clinical Departments, Daulby Street, Liverpool, L69 3GA, UK.
Alzbeta
A
Chorvatova
Munir
M
Hussain
D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D006352:Heart Ventricles / Q000166:cytology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000502:physiology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D010726:Phosphodiesterase Inhibitors; D015221:Potassium Channels; D002110:Caffeine; D011188:Potassium