K + channels in cultured bovine retinal pericytes: Effects of β-adrenergic stimulation

Abstract

Retinal pericytes are key cells involved in the regulation of retinal blood flow. The purpose of this work was to identify the K + channel population expressed in cultured bovine retinal pericytes and to determine whether β-adrenergic stimulation alters the activity of these channels. Isolated pericytes were obtained by homogenization and filtration of bovine retina and K + channels were studied with the whole-cell configuration of the patch-clamp technique on 3-5 passaged pericytes. Pericytes expressed an inward current dependent on extracellular K + concentration which was sensitive to micromolar concentrations of barium, a characteristic of an inward-rectifying K + current. Furthermore, two voltage-dependent outward currents were also observed. Their activation and inactivation properties, as well as their respective sensitivity to 4-aminopyridine and iberiotoxin, were indicative of voltage-sensitive and large-conductance calcium-activated K + channels (BK Ca). Isoproterenol and dibutyryl cyclic adenosine monophosphate enhanced the activity of BK Ca without affecting the other potassium currents. In conclusion, bovine retinal pericytes express mainly two outward potassium currents, K v and BK Ca, as well as an inward rectifying K + current, K ir. Physiologic stimuli such as an increase in extracellular potassium concentration or β-adrenergic receptor stimulation enhance the activity of K ir and BK Ca, respectively, suggesting a potential role for these channels in the control of retinal blood flow.