Details

Autor(en) / Beteiligte

• Albert, A. P.
• Large, W. A.

Titel

Inhibitory regulation of constitutive transient receptor potential-like cation channels in rabbit ear artery myocytes

Ist Teil von

• The Journal of physiology, 2004-10, Vol.560 (1), p.169-180

Ort / Verlag

9600 Garsington Road , Oxford , OX4 2DQ , UK: The Physiological Society

Erscheinungsjahr

2004

Quelle

MEDLINE

Beschreibungen/Notizen

• In the present study we have investigated an inhibitory pathway regulating a constitutively active Ca 2+ -permeable non-selective cation conductance ( I cat ) in rabbit ear artery smooth muscle cells. Constitutive single channel activity of I cat was recorded in cell-attached and inside-out patches with similar unitary conductance values. In inside-out patches with relatively high constitutive activity the G-protein activator GTPγS inhibited channel activity which was reversed by the protein kinase C (PKC) inhibitor chelerythrine indicating a G-protein pathway inhibits channel activity via PKC. Spontaneous channel activity was also suppressed by the G-protein inhibitor GDPβS suggesting a G-protein is also involved in initiation of constitutive channel activity. Bath application of antibodies to G αq /G α11 enhanced channel activity whereas anti-G α1−3 /G αo antibodies decreased basal channel activity which suggests that G αq /G α11 and G αι /G αo proteins initiate, respectively, the inhibitory and excitatory cascades. The phospholipase C (PLC) inhibitor U73122 increased spontaneous activity which implies a role for PLC in the inhibitory pathway. Bath application of the diacylycerol (DAG) analogue 1-oeoyl-2-acetyl- sn- glycerol (OAG) decreased the probability of channel opening ( NP o ) and this was reversed by chelerythrine. Application of the PKC activator phorbol 12, 13-dibutyrate (PDBu) and chelerythrine, respectively, decreased and increased NP o . These data indicate that spontaneously active cation channels are inhibited by a tonic inhibitory pathway involving G αq /G α11 -mediated stimulation of PLC to generate DAG which activates PKC to inhibit channel opening. There were some patches with relatively low NP o and it was evident that the inhibitory pathway was particularly marked in these cases. Moreover in the latter patches GTPγS and OAG caused marked increases in NP o . Together with inhibitory effects of GDPβS and anti-G α1−3 /G αo antibodies the results suggest that there is constitutive G αi /G αo protein activity leading to channel opening via a DAG-mediated but PKC-independent mechanism. Finally, with whole-cell recording it is shown that noradrenaline increases I cat and the noradrenaline-evoked response is markedly potentiated by PKC inhibition. This latter observation shows that PKC also limits agonist-evoked I cat in these arterial myocytes.