Basal nonselective cation permeability in rat cardiac microvascular endothelial cells.
The presence of a basal nonselective cation permeability was mainly investigated in primary cultures of rat cardiac microvascular endothelial cells (CMEC) by applying both the patch-clamp technique and Fura-2 microfluorimetry. With low EGTA in the pipette solution, the resting membrane potential of CMEC was -21.2 +/- 1.1 mV, and a Ca(2+)-activated Cl(-) conductance was present. When the intracellular Ca(2+) was buffered with high EGTA, the membrane potential decreased to 5.5 +/- 1.2 mV. In this condition, full or partial substitution of external Na(+) by NMDG(+) proportionally reduced the inward component of the basal I-V relationship. This current was dependent on extracellular monovalent cations with a permeability sequence of K(+) > Cs(+) > Na(+) > Li(+) and was inhibited by Ca(2+), La(3+), Gd(3+), and amiloride. The K(+)/Na(+) permeability ratio, determined using the Goldman-Hodgkin-Katz equation, was 2.01. The outward component of the basal I-V relationship was reduced when intracellular K(+) was replaced by NMDG(+), but was not sensitive to substitution by Cs(+). Finally, microfluorimetric experiments indicated the existence of a basal Ca(2+) entry pathway, inhibited by La(3+) and Gd(3+). The basal nonselective cation permeability in CMEC could be involved both in the control of myocardial ionic homeostasis, according to the model of the blood-heart barrier, and in the modulation of Ca(2+)-dependent processes.
Department of Physiological and Pharmacological Sciences, University of Pavia, 27100 Pavia, Italy.
Francesco
F
Moccia
Roberto
R
Berra-Romani
Silvana
S
Baruffi
Santina
S
Spaggiari
David J
DJ
Adams
Vanni
V
Taglietti
Franco
F
Tanzi
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002412:Cations; D002478:Cells, Cultured; D004594:Electrophysiology; D004730:Endothelium, Vascular / Q000166:cytology*; D005470:Fluorometry; D009206:Myocardium / Q000166:cytology*; D018408:Patch-Clamp Techniques; D010539:Permeability; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D013997:Time Factors
D002412:Cations; D012964:Sodium; D011188:Potassium; D002118:Calcium