J. Jurevicius et R. Fischmeister, LONGITUDINAL DISTRIBUTION OF NA-ADRENOCEPTORS ON THE SARCOLEMMAL MEMBRANE OF FROG CARDIOMYOCYTES( AND CA2+ CHANNELS AND BETA), Journal of physiology, 503(3), 1997, pp. 471-477
1. The distribution of L-type Ca2+ and tetrodotoxin-sensitive Na+ chan
nels and of beta-adrenergic receptors was examined in frog ventricular
myocytes using tile whole-cell patch-clamp technique and a double cap
illary for extracellular microperfusion. 2. Rod-shaped cells (250-300
mu m long) were sealed at both ends to two patch-clamp pipettes and po
sitioned transversally at different positions between the mouths of tw
o microcapillaries separated by a thin wall. A combination of nifedipi
ne (1 mu M) and tetrodotoxin (0.3 mu M) (blocking solution) was added
to one capillary in order to inhibit macroscopic Ca2+ and Na+ currents
(I-Ca and I-Na, respectively) in the part of the cell exposed to this
capillary. 3. Moving the cell in 10-20 mu m steps from the control ca
pillary to the capillary containing the blocking solution induced step
decreases in I-Ca and I-Na amplitudes. Complete block of both current
s occurred when the entire cell was exposed to the blocking solution.
4. Each step decrease in current was due to the los of activity of the
functional Ca2+ and Na+ channels present in the slice of sarcolemmal
membrane newly exposed to the blocking solution. These step current ch
anges allowed longitudinal mapping of current density for Ca2+ and Na channels on the sarcolemmal membrane. 5. Addition of a submaximal con
centration of isoprenaline (10 nM) to the control capillary induced a
local increase in I-Ca which enabled examination of the distribution o
f functional beta-adrenergic receptors as well. 6. Our results demonst
rate that Ca2+ and Na+ channels and beta-adrenergic receptors are equa
lly and essentially uniformly distributed on the sarcolemmal membrane
of frog ventricular myocytes.