Stretch-activated currents in ventricular myocytes: amplitude and arrhythmogenic effects increase with hypertrophy.

BACKGROUND

Mechanical dilation of the human ventricle is known to induce arrhythmias, the underlying ionic mechanisms, however, remain to be clarified.

METHODS

Ventricular myocytes isolated from human, guinea-pig or rat hearts were stretched between the patch electrode and a glass stylus.

RESULTS

Local stretch prolonged the action potential, depolarized the resting membrane and caused extra systoles. Under voltage-clamp conditions, stretch activated several ionic current components. The most prominent current was a stretch activated current (I(SAC)) through non-selective cation channels. I(SAC) followed a linear voltage-dependence, reversed polarity close to 0 mV and was suppressed by 5 microM Gd(3+). During stretch, I(SAC) became steady within 200 ms. I(SAC) did not inactivate and it completely disappeared upon relaxation. Stretch-sensitivity was evaluated from the slope of I(SAC) versus amplitude of stretch. Stretch sensitivity was 75 pA/microm in myocytes from young (3 month), 143 pA/microm in myocytes from old (15 months), and 306 pA/microm in hypertrophied myocytes from old (15 months) spontaneously hypertensive animals. Stretch sensitivity was 262 pA/microm in hypertrophied myocytes from human failing hearts, and it was 143 pA/microm in guinea-pig ventricular myocytes.

CONCLUSIONS

Local stretch of adult single ventricular myocytes can induce arrhythmias that resemble surface-recordings from whole hearts. Stretch modulates multiple current components, I(SAC) being the current with the largest arrhythmogenic potential. Stretch-sensitivity of I(SAC) is higher in hypertrophied than in control myocytes as can be expected from the observation that hypertrophy and failure increase the risk of stretch-induced arrhythmias.