Xiaofen Liu, and the University of Alabama at Birmingham Animal Resources Program for technical assistance with the frog surgeries. clamp. T26A and T26E did not exhibit acid-activated currents. S40A was indistinguishable from wild type (WT), whereas S40E, S499A, and S499D currents were decreased. The PKC activators PMA and phorbol 12, 13-dibutyrate inhibited WT hASIC1b and S499A, and PMA had no effect on S40A or on WT hASIC1b in oocytes pretreated with the PKC inhibitor chelerythrine. Chelerythrine inhibited WT hASIC1b and S40A but had no effect on S499A or S40A/S499A. PKC activators or the inhibitor did not affect the surface expression of WT hASIC1b. These data show that the two PKC consensus sites S40 and S499 differentially regulate hASIC1b and mediate the effects of PKC activation or PKC inhibition on hASIC1b. This will result in a deeper understanding of PKC regulation of this channel in glioma cells, information that may help in designing potentially beneficial therapies in their treatment. Keywords:two-electrode voltage clamp;Xenopus laevisoocytes; phorbol 12-myristate 13-acetate; chelerythrine; mutagenesis; phorbol 12,13-dibutyrate; protein kinase C acid-sensing ion channels(ASICs) are activated by extracellular protons and belong to the epithelial Na+channel (ENaC)/degenerin (Deg) Biotinyl Cystamine family of ion channels. Four ASIC genes (ASIC1ASIC4) have been cloned, and ASIC1ASIC3 have splice variants (19,28,29,31,42). ASICs are permeable to Na+but also to other monovalent and divalent cations like Ca2+(in the case of ASIC1), Li+, K+, and H+(41,42). ASIC subunits are expressed in peripheral nervous system neurons, where they have been implicated in nociception during tissue acidosis and in mechanosensation (42). In the central nervous system (CNS), ASIC1 has been mostly studied in mouse and rat brains, where it is abundantly expressed, and ASIC1a, ASIC1b, and ASIC2 have been found to be expressed in the human brain (17). Mouse ASIC1a modulates synaptic plasticity, contributing to learning, memory, and fear conditioning (42). ASICs are also expressed in non-neuronal tissue and cells such as the retina, osteoblasts, ear, taste buds, lung, testis, astrocytes, and intestine, where they may sense extracellular acid changes (38,42). The recent crystallization of chicken ASIC1 at low pH has confirmed the protein structure and has also revealed that Gfap ASIC1 forms a homotrimer (26). The protein consists of short intracellular NH2and COOH termini, two transmembrane-spanning -helixes, and a large extracellular loop (28,29,40,42). Different ASIC subunits are Biotinyl Cystamine capable of forming heteromultimers with other ASIC subunits and, in some cases, with other ENaC/Deg subunits (2,4,5,15,32). The extracellular domain senses protons and interacts with modulators, including proteases, Zn2+, Ca2+, and redox reagents (42). The cytoplasmic NH2and COOH termini contain phosphorylation sites and interact with other proteins such as protein interacting with C kinase 1 (PICK1) (14,25,42), postsynaptic density protein 95, abnormal cell lineage 7b (24), and annexin (13), resulting in changes in the current density or cellular localization of ASIC. For example, PICK1 increases the ASIC2a current amplitude by potentiating the phosphorylation of ASIC2a at T39 [equivalent to site S40 on human (h)ASIC1b] (3). Also, PKC phosphorylation of the COOH terminus of ASIC3 (at S523) increases the binding of ASIC3 to Na+/H+exchanger regulatory factor 1, which, in turn, increases the current of ASIC3 expressed inXenopusoocytes (12). Furthermore, PKA phosphorylates hASIC1b at S479, and this phosphorylation interferes with PICK1 binding (30). Berdiev et al. (6) showed that PKC holoenzyme phosphorylates hASIC1b in vitro, and the addition of PKC to the intracellular side of hASIC1b in lipid bilayers decreases its open probability. Generally, the direction of the effect of PKC on ion channels is cell type specific and channel subtype specific, with PKC activation resulting in either an increase or a decrease of the current (11). For example, the activation Biotinyl Cystamine of PKC increased transepithelial Na+transport measured as amiloride-sensitive short-circuit current (Isc) across the skins of.