Regional differences in electrical and mechanical properties of myocytes from guinea-pig hearts with mild left ventricular hypertrophy.
OBJECTIVE
To investigate electrical and mechanical properties of single myocytes isolated from different regions of the left ventricle in control and hypertrophied hearts.


METHODS
Mild cardiac hypertrophy was induced in guinea-pigs by aortic constriction. Myocytes were isolated from basal sub-endocardial, basal mid-myocardial and apical sub-epicardial layers of the left ventricle. Action potentials were stimulated at 1 Hz. Membrane currents were measured using the switch-clamp technique. Cell shortening was measured using a photodiode array.


RESULTS
In control hearts mean action potential duration (APD) was longer in sub-endocardial myocytes than in sub-epicardial myocytes. In hypertrophy APD was prolonged in sub-epicardial and mid-myocardial myocytes and unchanged in sub-endocardial myocytes (APD90 ms, control: sub-endocardial 273 +/- 12, mid-myocardial 254 +/- 14, sub-epicardial 229 +/- 9; hypertrophy: sub-endocardial 259 +/- 13, mid-myocardial 291 +/- 9, sub-epicardial 268 +/- 11, P < 0.005, ANOVA). There was no significant regional difference in APD in hypertrophied hearts. In control hearts L-type calcium current (ICa) was similar in all regions. In hypertrophy ICa was increased in sub-epicardial and mid-myocardial myocytes and reduced in sub-endocardial myocytes. Calcium-activated tail currents were not regionally different in control or hypertrophied hearts, but were increased in hypertrophy.


CONCLUSIONS
Changes in electrical and mechanical properties associated with hypertrophy are not homogeneous throughout the left ventricle. The difference in APD between sub-endocardial and sub-epicardial myocytes seen in control hearts is lost in hypertrophy. These results may favour the propagation of re-entry arrhythmias in hypertrophied hearts.
Bryant
S M
SM
Department of Cardiovascular Medicine, University of Oxford, John Radcliffe Hospital, UK.
Shipsey
S J
SJ
Hart
G
G
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D015220:Calcium Channels / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology; D048429:Cell Size / Q000502:physiology; D004553:Electric Conductivity; D004699:Endocardium / Q000503:physiopathology; D005260:Female; D006168:Guinea Pigs; D006321:Heart / Q000503:physiopathology*; D017379:Hypertrophy, Left Ventricular / Q000503:physiopathology*; D018408:Patch-Clamp Techniques; D010496:Pericardium / Q000503:physiopathology
D015220:Calcium Channels