Functional Expression of TRPV4 Cation Channels in Human Mast Cell Line (HMC-1)

Abstract

Mast cells are activated by specific allergens and also by various nonspecific stimuli, which might induce physical urticaria. This study investigated the functional expression of temperature sensitive transient receptor potential vanilloid (TRPV) subfamily in the human mast cell line (HMC-1) using whole-cell patch clamp techniques. The temperature of perfusate was raised from room temperature (RT, 23 similar to 25 degrees C) to a moderately high temperature (MHT, 37 similar to 39 degrees C) to activate TRPV3/4, a high temperature (HT, 44 similar to 46 degrees C) to activate TRPV1, or a very high temperature (VHT, 53 similar to 55 degrees C) to activate TRPV2. The membrane conductance of HMC-1 was increased by MHT and HT in about 50% (21 of 40) of the tested cells, and the I/V curves showed weak outward rectification. VHT-induced current was 10-fold larger than those induced by MHT and HT. The application of the TRPV4 activator 4 alpha - phorbol 12,13-didecanoate (4 alpha PDD, 1 mu M) induced weakly outward rectifying currents similar to those induced by MHT. However, the TRPV3 agonist camphor or TRPV1 agonist capsaicin had no effect. RT-PCR analysis of HMC-1 demonstrated the expression of TRPV4 as well as potent expression of TRPV2. The [Ca(2+)](c) of HMC-1 cells was also increased by MHT or by 4 alpha PDD. In summary, our present study indicates that HMC-1 cells express Ca(2+)-permeable TRPV4 channels in addition to the previously reported expression of TRPV2 with a higher threshold of activating temperature.