Objectives: 

Activation of Ca2+-activated chloride channels (CACCs) is an important excitatory mechanism in vascular myocytes, which leads to Cl- ion efflux and membrane depolarisation that is sufficient to enhance voltage gated Ca2+ channels activity. The present study aimed to ascertain the electrophysiological effects of the novel TMEM16A inhibitor T16Ainh-AO1 and TMEM16A potentiator tetrazolylbenzamide (Fact), as well as the conventional CACC blocker niflumic acid (NFA) on CACC currents (IClCa) in pulmonary artery (PA) myocytes.

Materials: 

Whole cell and single channel electrophysiological recordings were carried out on freshly isolated PA myocytes, from New Zealand White rabbits (2-2.5 kg). In whole cell configuration, IClca was evoked by pipette solutions of known free Ca2+ (100-500nM) immediately after rupture of the seal. Upon stabilisation of the IClca current voltage (IV) relationships were constructed by stepping from a holding potential (-50mV) to a test potential between -100mV and +100mV for 1s. Single channel recordings were also made in the outside-out patch clamp configuration using pipette solutions containing either 100nM or 500nM free Ca2+.

Results: 

In 500nM [Ca2+]i, 10mM and 100mM NFA produced inhibition and potentiation of whole cell IClca as reported previously. In contrast, the novel TMEM16A inhibitor T16Ainh-AO1 (1-30mM) produced a simple inhibition of IClca. Co-application of 10mM NFA after T16Ainh-AO1 augmented the IClca at certain voltages. Fact augmented IClca significantly at 100nM and 250nM [Ca2+]i, but not at 500nM [Ca2+]i. Similar effects of T16Ainh-AO1 and Fact were observed on single CACC channel activity.

Conclusions: 

This study provides pharmacological evidence that TMEM16A channel proteins are likely to contribute to CACCs in rabbit pulmonary artery myocytes.