A polycystin-2-like large conductance cation channel in rat left ventricular myocytes.
OBJECTIVE
Several members of the PKD gene family (PKD2, PKDL and PKD2L2) are expressed in the heart. Polycystin-2 and its homologues, which are encoded by these genes, have recently been shown to form Ca(2+)-regulated nonselective cation channels in heterologous expression systems. Previously, large conductance nonselective cation channels (LCC) have been described in cardiomyocytes, however, their molecular identity remained obscure. We therefore examined whether LCCs may be formed by polycystins.


METHODS
Myocytes isolated from the rat left ventricle were investigated by the whole-cell patch-clamp technique and single-cell RT-PCR.


RESULTS
Application of 10 mM caffeine to the bath solution to increase the intracellular Ca(2+) concentration led to activation of LCC in 56% of the myocytes investigated (total n=651), in approximately 10%, more than three LCCs were detected. The single channel conductance was approximately 300 pS for monovalent cations and the channel was relatively nonselective for the monovalent cations Na(+), K(+), Li(+), and Cs(+) and also permeable for the divalent cations Ca(2+) and Ba(2+), but impermeable for NMDG(+) and Cl(-). Amiloride (IC(50)=131+/-1.1 microM) and millimolar concentrations of the trivalent cations Gd(3+) and La(3+) inhibited the LCC. Single-cell RT-PCR analysis revealed that mRNA of PKD2 and PKD2L2, but not PKDL or PKD1 are expressed in individual rat left ventricular myocytes.


CONCLUSIONS
The characteristics of LCC shown in the present study are nearly identical to those observed for polycystin-2 and its homologues suggesting that polycystin-2 or polycystin-2L2 underlie LCC in ventricular myocytes.
Volk
Tilmann
T
Institut für Physiologie, Universitätskrankenhaus Hamburg-Eppendorf, Universität Hamburg, Germany. volk@uke.uni.hamburg.de
Schwoerer
Alexander Peter
AP
Thiessen
Susanne
S
Schultz
Jobst-Hendrik
JH
Ehmke
Heimo
H
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism*; D004232:Diuretics / Q000494:pharmacology; D005260:Female; D005682:Gadolinium / Q000494:pharmacology; D006352:Heart Ventricles; D007811:Lanthanum / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050396:TRPP Cation Channels
D000584:Amiloride; D002110:Caffeine; D002118:Calcium; D020746:Calcium Channels, L-Type; D004232:Diuretics; D005682:Gadolinium; D007811:Lanthanum; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D010726:Phosphodiesterase Inhibitors; D012333:RNA, Messenger; D050396:TRPP Cation Channels