Selective blockade of the intermediate-conductance Ca2+-activated K+ channel suppresses proliferation of microvascular and macrovascular endothelial cells and angiogenesis in vivo.
OBJECTIVE
Ca2+-activated K+ (K(Ca)) channels have been proposed to promote mitogenesis in several cell types. Here, we tested whether the intermediate-conductance K(Ca) channel (IKCa1) and the large-conductance K(Ca) channel (BK(Ca)) contribute to endothelial cell (EC) proliferation and angiogenesis.


RESULTS
Function and expression of IKCa1 and BK(Ca)/Slo were investigated by patch-clamp analysis and real-time RT-PCR in human umbilical vein ECs (HUVECs) and in dermal human microvascular ECs 1 (HMEC-1). HMEC-1 expressed IKCa1 and BK(Ca)/Slo, whereas HUVECs expressed IKCa1. A 48-hour exposure to basic fibroblast growth factor (bFGF) augmented IKCa1 current amplitudes and induced a 3-fold increase in IKCa1 mRNA expression in HUVECs and HMEC-1. Vascular endothelial growth factor (VEGF) was also effective in upregulating IKCa1. BK(Ca)/Slo expression and current amplitudes in HMEC-1 were not altered by bFGF. bFGF- and VEGF-induced EC proliferation was suppressed by charybdotoxin, clotrimazole, or the selective IKCa1 blocker 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34), whereas inhibition of BK(Ca)/Slo by iberiotoxin was ineffective. In the Matrigel plug assay in mice, administration of TRAM-34 for 2 weeks significantly suppressed angiogenesis by approximately 85%.


CONCLUSIONS
bFGF and VEGF upregulate expression of IKCa1 in human ECs. This upregulation of IKCa1 seems to be required for mitogen-induced EC proliferation and angiogenesis in vivo. Selective IKCa1 blocker might be of therapeutic value to prevent tumor angiogenesis.
Grgic
Ivica
I
Department of Nephrology, Charité, Campus Benjamin Franklin, Berlin, Germany.
Eichler
Ines
I
Heinau
Philipp
P
Si
Han
H
Brakemeier
Susanne
S
Hoyer
Joachim
J
Köhler
Ralf
R
D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D003022:Clotrimazole / Q000494:pharmacology*; D004730:Endothelium, Vascular / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008833:Microcirculation; D018919:Neovascularization, Physiologic / Q000187:drug effects*; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000502:physiology; D011720:Pyrazoles / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D014471:Umbilical Veins / Q000166:cytology
D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496923:KCNN4 protein, human; D051036:Large-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D011720:Pyrazoles; D012333:RNA, Messenger; C411671:TRAM 34; D003022:Clotrimazole