Comparison between spontaneously beating atria from control and streptozocin-diabetic rats.

Isolated spontaneously beating atria from streptozocin diabetic rats were compared with those from controls. Diabetic atria were found to have reduced rates, increased forces of contraction and reduced sensitivity to the inotropic effects of noradrenaline, isoprenaline, tyramine and calcium. Positive chronotropic responses to tyramine were also reduced but those to noradrenaline and isoprenaline were increased suggesting that tyramine releasable stores of noradrenaline were reduced. Elevation of glucose concentration in the medium from 5.6 to 27 mM resulted in decrease of inotropic sensitivity to the agents used in both control and diabetic rat atria. Resting contractile force of control rat atria was reduced by the inclusion of either 22 mM 2-deoxyglucose, 10(-3) i.u. insulin ml-1 or 5 mM acetate in the medium. The rate was also reduced by medium containing 2-deoxyglucose but increased by insulin. 2-Deoxyglucose also reduced inotropic but increased chronotropic sensitivity to isoprenaline. Possible mechanisms responsible for the changes observed are discussed.