Sarcoplasmic reticulum K(+) channels from human and sheep atrial cells display a specific electro-pharmacological profile.
It has recently been proposed that the Ca(2+) uptake by the SR is inhibited by blocking Cl(-) and/or K(+) movements across this intracellular membrane. We have characterised the functional and pharmacological profile of the SR K(+) channel derived from human and sheep atrial cells. Mammalian atrial SR preparations were subjected to [(3)H]-ryanodine binding assays, SDS-PAGE analysis and channel protein reconstitution into planar lipid bilayers. Assessment of [(3)H]-ryanodine binding on the SR Ca(2+) release channel revealed that it was inhibited by both Ruthenium Red and Mg(2+) with IC(50) values of 4.11 microM and 9.12 m M, respectively. In crude populations as well as in all SR-enriched fractions, activity of K(+) selective channels was recorded. This channel displayed a high conductance value of 193 and 185 pS for human and sheep preparations respectively. Gating and conducting behaviours of this channel were unaffected by the addition of up to 5m M 4-Aminopyridine (4-AP), 100 n M Iberiotoxin (IbTX), 10 microM E-4031 and 30 microM amiodarone. However, 100n M Dendrotoxin (gamma-DTX) largely increase the occurrence of the SR K(+) channel subconducting states without an effect on the main unitary conductance. These results demonstrate that the SR K(+) channel, present in all mammalian atrial SR membranes tested (as assessed by [(3)H]-ryanodine binding and its typical inhibition by ruthenium red and the magnesium), displays different properties than those classically described for cardiac sarcolemmal K(+) channels. Despite the fact that the biophysical properties of the SR K(+) channel are well known, its molecular identity remains to be ascertained.
Picard
Luc
L
Le Bilarium, Département de Physiologie et Biophysique, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, QC, J1H 5N4, Canada.
Côté
Karel
K
Teijeira
Javier
J
Greentree
David
D
Rousseau
Eric
E
D000818:Animals; D002648:Child; D004546:Elapid Venoms / Q000494:pharmacology; D004553:Electric Conductivity; D006325:Heart Atria / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D015640:Ion Channel Gating; D008274:Magnesium / Q000494:pharmacology; D032383:Myocytes, Cardiac / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects*; D012430:Ruthenium Red / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D012756:Sheep
D004546:Elapid Venoms; D015221:Potassium Channels; D012430:Ruthenium Red; D012433:Ryanodine; C020273:dendrotoxin; D008274:Magnesium