(Hypertension. 1995;26:1060-1064.)
© 1995 American Heart Association, Inc.
Articles |
Augmented Calcium Currents in Mesenteric Artery Branches of the Spontaneously Hypertensive Rat
From Bockus Research Institute, The Graduate Hospital, and the Department of Physiology, University of Pennsylvania, Philadelphia.
Abstract The greater efficacy of organic channel blockers in
lowering peripheral resistance and blood pressure in
hypertensive subjects has been suggested to be the result of augmented
calcium influx through L-type calcium channels in arterial
smooth muscle. These studies were performed to determine whether
differences exist in voltage-gated calcium channels of mesenteric
artery branches from 20-week-old spontaneously hypertensive rats
(SHR) compared with Wistar-Kyoto rats (WKY). Single myocytes were
acutely isolated by collagenase and elastase treatment
and studied at room temperature (
20°C) with the use of
whole-cell, patch-clamp methods. Maximum values of calcium
current measured at 0 mV from a holding potential of -90 mV were
larger in SHR myocytes (105±11 versus 149±15 pA). Values of cell
capacitance were smaller in SHR (29.5±1.3 pF) compared with WKY
(35.0±1.5 pF) myocytes. Cell capacitance measures surface membrane
area and, when used to normalize calcium currents, magnified the
difference between WKY and SHR to approximately 47%. There was a
larger percent reduction of maximum calcium current at holding
potentials of -60 and -40 mV in SHR compared with WKY
myocytes: for example, at -40 mV calcium current was reduced from
values at -90 mV by -73±2% in SHR compared with
-58±1% in WKY. When divided by the maximum current for each
holding potential, the voltage dependence of normalized calcium
currents for the two groups was completely superimposed. Difference
currents were calculated by subtracting currents measured from holding
potentials of -90 and -40 mV. The voltage dependence of
difference currents was identical to that of the calcium currents
measured from the two values of holding potential. The results of this
study indicate that (1) only L-type calcium currents are present in
freshly isolated mesenteric artery myocytes from 20-week-old WKY
and SHR, and (2) these currents are larger in SHR. These differences in
calcium currents may contribute to augmented contractile responses that
have been previously reported.
Key Words: patch-clamp techniques • calcium channels • rats, inbred SHR
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