Bradykinin-induced potassium current in cultured bovine aortic endothelial cells

Effects of vasoactive agonists on the membrane potential of cultured bovine aortic and guinea-pig coronary endothelium

1. The effects of bradykinin, ATP, adenosine, histamine and thrombin on the membrane potential of confluent monolayers of cultured bovine aortic endothelial cells (BAECs) and guinea-pig coronary endothelial cells (GCECs) were studied at 37 degrees C using the whole-cell mode of the patch-clamp technique. 2. The amplitude histogram of the resting potentials of BAEC monolayers showed a bimodal distribution with one peak around -25 mV and another peak around -85 mV. Transitions from one potential level to the other were observed. The bistable membrane potential can be explained by an N-shaped current-voltage relation of the endothelial cell membrane. 3. When BAECs with a low resting potential (-10 to -30 mV) were superfused with maximally effective concentrations of ATP (2-10 microM) an initial hyperpolarization of -80 to -90 mV was observed which decayed to a plateau of about -60 mV within 1 min. When ATP was removed after 2-3 min the membrane potential returned to control level within 1 min. This was followed by a second hyperpolarization of 10-20 mV, which decayed within 15 min. 4. In the absence of extracellular calcium, ATP produced only a brief transient hyperpolarization in aortic endothelium. The plateau and the secondary hyperpolarization were abolished. These findings are consistent with the idea that the changes in membrane potential reflect changes in intracellular free Ca2+ and that the initial peak is due to release of Ca2+ from intracellular stores, whereas the plateau and the secondary hyperpolarization depend on transmembrane Ca2+ influx. 5. Bradykinin evoked potential changes similar to ATP in BAECs, except that the secondary hyperpolarization during wash-out was absent. When the membrane potential was more negative than -80 mV, ATP and bradykinin induced only a small initial hyperpolarization followed by a depolarization of up to 20 mV. 6. In aortic endothelium, ADP (10 microM) evoked a much smaller response than ATP. Adenosine (10 microM), thrombin (2 units/ml), acetylcholine (10 microM) and histamine (10 microM) had only a very small effect on the membrane potential, if any. 7. The amplitude histogram of the membrane potential of GCECs showed only one peak around -35 mV. In coronary endothelium, application of bradykinin, ATP, histamine, thrombin, acetylcholine and adenosine all evoked a transient hyperpolarization of 10-40 mV lasting 1 min or less, which then turned into a depolarization. 8. The K+ channel openers cromakalim (BRL 34915) and lemakalim (BRL 38227) did not affect the membrane potential of GCECs or BAECs.(ABSTRACT TRUNCATED AT 400 WORDS)

Angiotensin II, vasopressin and GTP[gamma-S] inhibit inward-rectifying K+ channels in porcine cerebral capillary endothelial cells

Cerebral capillaries from porcine brain were isolated, and endothelial cells were grown in primary culture. The whole-cell tight seal patch-clamp method was applied to freshly isolated single endothelial cells, and cells which were held in culture up to one week. With high K+ solution in the patch pipette and in the bath we observed inward-rectifying K+ currents, showing a time-dependent decay in part of the experiments. Ba2+ (1-10 mM) in the bath blocked this current, whereas outside tetraethylammonium (10 mM) decreased the peak current but increased the steady-state current. Addition of 1 microM of angiotensin II or of arginine-vasopressin to the extracellular side caused a time-dependent inhibition of the inward-rectifying K+ current in part of the experiments. Addition of 100 microM GTP[gamma-S] to the patch pipette blocked the K+ inward rectifier. In cell-attached membrane patches two types of single inward-rectifying K+ channels were observed, with single channel conductances of 7 and 35 pS. Cell-attached patches were also obtained at the antiluminal membrane of intact isolated cerebral capillaries. Only one type of K+ channel with g = 30 pS was recorded. In conclusion, inwardly rectifying K+ channels, which can be inhibited by extracellular angiotensin II and arginine-vasopressin, are present in cerebral capillary endothelial cells. The inhibition of this K+ conductance by GTP[gamma-S] indicates that G-proteins are involved in channel regulation. It is suggested that angiotensin II and vasopressin regulate K+ transport across the blood-brain barrier, mediating their effects via G-proteins.

Cytosolic calcium ion regulation in cultured endothelial cells

Mechanisms involved in Ca2+ homeostasis and stimulus-secretion coupling in cultured endothelial cells in response to humoral and physical stimuli include passive leak, activation of ion channels, and chemical second messengers. Calcium entry is controlled by receptor activation, passive leak, and mechanical stretch. The rate at which Ca2+ enters the cell through these pathways is dependent on the transmembrane potential which governs the electrochemical gradient for Ca2+ and which is set by participation of various K channels.