B. Nilius et al., HISTAMINE-ACTIVATED, NONSELECTIVE CATION CURRENTS AND CA2-CELLS FROM HUMAN UMBILICAL VEIN( TRANSIENTS IN ENDOTHELIAL), Pflugers Archiv, 424(3-4), 1993, pp. 285-293
Permeation properties and modulation of an ionic current gated by hist
amine were measured in single endothelial cells from human umbilical c
ord veins by use of the patch-clamp technique in the ruptured-whole-ce
ll mode or using perforated patches. We combined these current measure
ments with a microfluorimetric method to measure concomitantly free in
tracellular calcium concentration (Ca2+!i). Application of histamine
induced an intracellular calcium transient and an ionic current that r
eversed near 0 mV. The amplitude of the current ranged from -0.2 to -2
nA at -100 mV. The tonic rise in Ca2+!i and the ionic current are pa
rtly due to Ca2+ influx. This Ca2+ entry pathway is also permeable for
Ba2+ and Mn2+. The amplitude of the histamine-activated current was a
lso closely correlated with the amplitude of the concomitant Ca2+ tran
sient, suggesting that the latter is at least partially due to Ca2+ in
flux through histamine-activated channels. The reversal potential of t
he histamine-induced current was 7.6 +/- 4.1 mV (n = 14) when the calc
ium concentration in the bath solution (Ca2+!o) was 1.5 mmol/l. With
10 mmol/l Ca2+!o it was -13.7 +/- 4.7 mV and shifted to + 13.0 +/- 1.
5 mV in nominally Ca2+-free solution (n = 3 cells). The amplitude of t
he current in Ca2+-free solution was enhanced compared to that in 10 m
mol/l Ca2+!o. The shift of the reversal potential and the concomitant
change of the current amplitude suggest that the channel is permeable
for calcium but has a smaller permeability for calcium than for monov
alent cations. The latency between the application of histamine and th
e appearance of the current was voltage dependent and was much smaller
at more negative potentials. This effect is unlikely to be due to des
ensitization, but may suggest a voltage-dependent step in the signal t
ransduction chain. Similar histamine-induced Ca2+ signals were observe
d if the currents were measured in patches perforated with nystatin. T
he onset of the agonist-activated current was, however, much more dela
yed and its amplitude significantly lower than in ruptured patches. Th
e histamine-induced currents and intracellular Ca2+-transients were la
rgely reduced after incubation of endothelial cells with the phorbol e
ster TPA. H7, a blocker of protein kinase C, induced membrane currents
and Ca2+ signals in the absence of an agonist. It is concluded that t
he agonist-activated Ca2+-entry in endothelial cells occurs through no
n-selective cation channels which can be down-regulated by protein kin
ase C activation.