Heterogeneous expression of Ca(2+) handling proteins in rabbit sinoatrial node.
We investigated the densities of the L-type Ca(2+) current, i(Ca,L), and various Ca(2+) handling proteins in rabbit sinoatrial (SA) node. The density of i(Ca,L), recorded with the whole-cell patch-clamp technique, varied widely in sinoatrial node cells. The density of i(Ca,L) was significantly (p<0.001) correlated with cell capacitance (measure of cell size) and the density was greater in larger cells (likely to be from the periphery of the SA node) than in smaller cells (likely to be from the center of the SA node). Immunocytochemical labeling of the L-type Ca(2+) channel, Na(+)-Ca(2+) exchanger, sarcoplasmic reticulum Ca(2+) release channel (RYR2), and sarcoplasmic reticulum Ca(2+) pump (SERCA2) also varied widely in SA node cells. In all cases there was significantly (p<0.05) denser labeling of cells from the periphery of the SA node than of cells from the center. In contrast, immunocytochemical labeling of the Na(+)-K(+) pump was similar in peripheral and central cells. We conclude that Ca(2+) handling proteins are sparse and poorly organized in the center of the SA node (normally the leading pacemaker site), whereas they are more abundant in the periphery (at the border of the SA node with the surrounding atrial muscle).
Musa
Hanny
H
School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom.
Lei
Ming
M
Honjo
Hauro
H
Jones
Sandra A
SA
Dobrzynski
Halina
H
Lancaster
Mathew K
MK
Takagishi
Yoshiko
Y
Henderson
Zaineb
Z
Kodama
Itsuo
I
Boyett
Mark R
MR
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000032:analysis*; D000252:Calcium-Transporting ATPases / Q000032:analysis; D007150:Immunohistochemistry; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel / Q000032:analysis; D012508:Sarcolemma / Q000737:chemistry; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019831:Sodium-Calcium Exchanger / Q000032:analysis; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis; D014018:Tissue Distribution
D020746:Calcium Channels, L-Type; D019837:Ryanodine Receptor Calcium Release Channel; D019831:Sodium-Calcium Exchanger; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium