Contractile properties of ventricular myocytes isolated from spontaneously hypertensive rat.
OBJECTIVE
To determine whether there are any differences in contractile properties of individual cardiac myocytes isolated from the spontaneously hypertensive rat (SHR) in comparison with its normotensive control--the Wistar-Kyoto (WKY) rat.


METHODS
The effects of cardiac hypertrophy upon individual myocytes from SHR have not been studied previously. Isolated cardiac myocytes do not suffer from a number of problems inherent in experiments on multicellular preparations.


METHODS
Seven SHR and eight WKY animals were studied. Age-matched animals were compared at 60 and 100 days old. Ventricular myocytes were isolated enzymatically. Myocyte length and width was measured. The cells were stimulated with extracellular electrodes and contraction was measured optically. The effects of altering stimulus rate and extracellular calcium concentration upon contraction were studied.


RESULTS
SHR myocytes were found to be significantly wider than WKY myocytes. The contraction (i.e. unloaded cell shortening) of SHR myocytes at stimulation rate of 0.3, 1, 2 and 3 Hz was significantly increased. The time-course of contraction was altered, with SHR myocytes having an increased maximal velocity of shortening and relaxation. The response to changes in bathing calcium was similar in both strains.


CONCLUSIONS
Individual cardiac myocytes isolated from SHR have an increased contraction. This indicates that cardiac hypertrophy, at least in the early stages, is a protective adaptation allowing the heart to overcome the increased afterload resulting from hypertension.
Brooksby
P
P
Department of Physiology, School of Medical Sciences, University of Bristol, UK.
Levi
A J
AJ
Jones
J V
JV
D000818:Animals; D002118:Calcium / Q000502:physiology; D002469:Cell Separation / Q000379:methods; D006973:Hypertension / Q000503:physiopathology; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000166:cytology; D051381:Rats; D011918:Rats, Inbred SHR / Q000502:physiology*; D011921:Rats, Inbred WKY; D013997:Time Factors; D016276:Ventricular Function
D002118:Calcium