Bovine versus rat adrenal chromaffin cells: Big differences in BK potassium channel properties

Both bovine and rat adrenal chromaffin cells have served as pioneering mode l systems in cellular neurophysiology, including in the study of large cond uctance calcium- and voltage-dependent K+ (BK) channels. We now report that while BK channels dominate the outward current profile of both species, sp ecific gating properties vary widely across cell populations, and the distr ibutions of these properties differ dramatically between species. Although BK channels were first described in bovine chromaffin cells, rapidly inacti vating ones were discovered in rat chromaffin cells. We report that bovine cells can also exhibit inactivating BK channels with varying properties sim ilar to those in rat cells. However, a much smaller proportion of bovine ce lls exhibit inactivating BK current, the proportion of the total current th at inactivates is usually smaller, and the rate of inactivation is often mu ch slower. Other gating features differ as well; the voltage dependence of channel activation is much more positive for bovine cells, and their rates of activation and deactivation are faster and slower, respectively. Modelin g studies suggest that channel heterogeneity is consistent with varying tet rameric combinations of inactivation-competent versus in-competent subunits . The results suggest that chromaffin BK channel functional nuances represe nt an important level for evolutionary tailoring of autonomic stress respon ses.