The objective of this study was to determine potential post‐pubertal gender‐specific differences in the contractility of papillary muscles, the electrophysiological properties and Ca²⁺ transients of freshly dissociated ventricular myocytes from the rat heart.

The contractions of rat papillary muscles from 2‐ to 14‐month‐old male and female rats were studied under isometric and isotonic conditions (29 °C). While the hearts of young (2–4 months) male and female rats displayed a similar contractile profile, papillary muscles of female rats aged 6 months and older exhibited smaller isometric and isotonic contractions, smaller maximal rates of tension and shortening development and decline (±DT/dt and ±DL/dt) velocities during both the onset and relaxation phases, and shorter contractions than age‐matched males.

To explore the possible cellular basis accounting for these differences, action potentials and macroscopic currents were recorded from freshly dissociated myocytes using the whole‐cell patch clamp technique (35 °C). Action potentials from male and female myocytes of 3‐ and 9‐month‐old rats did not vary as a function of age or gender. Consistent with these results, the magnitude (expressed in pA pF⁻¹), voltage‐dependence and kinetics of the inward rectifier (I_K1), transient outward (I_to) and sustained (I_K) K⁺ currents displayed little, if any dependence on age or gender.

L‐type Ca²⁺ current (I_Ca(L)) measured in caesium‐loaded myocytes (35 °C) from male and female rats of 3, 6 and 9 months of age exhibited similar characteristics. In contrast, while Ca²⁺ transients measured with indo‐1 were similar between 3‐month‐old male and female rat myocytes, Ca²⁺ transients of 10‐month‐old female myocytes were significantly reduced and showed a diminished rate of relaxation in comparison with those recorded in male rats of similar age.

These results suggest that important gender‐related changes in excitation‐contraction coupling occur following puberty, probably due to differences in Ca²⁺ handling capabilities at the level of the sarcoplasmic reticulum.