Narenjkar, Jamshid; (1998) The role of k+ channels in the signal transduction mechanisms of antigen-induced degranulation in the rat basophilic leukaemia (rbl-2h3) cell line. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

To investigate whether potassium channels are involved in the signal transduction mechanisms of antigen-stimulated mediator release in the rat basophilic leukaemia cell line (RBL-2H3), the effect of some potassium channel modulators on antigen-stimulated β- hexosaminidase secretion, membrane potential changes, 86Rb*-efflux and [Ca2+]i have been evaluated. Quinidine, a nonspecific K+ channel blocker, dose-dependently inhibited antigen induced 86Rb+-efflux, membrane repolarisation and secretion. Ba2+ inhibited antigen-induced secretion, but it had no effect on resting and antigen-stimulated 86Rb+-efflux, and it caused a massive depolarisation by itself. These data indicate that the inhibitory effect of quinidine may be due to the inhibition of channels, whereas the effect of Ba2+ might be either direct, by interfering with Ca2+ influx, or indirect, by causing depolarisation. Cetiedil and charybdotoxin inhibited β-hexosaminidase release with an IC50 of 84uM and 130uM respectively. Some recently synthesised cetiedil-related compounds ("UCL compounds") have also been tested. All the UCL compounds inhibited the antigen-stimulated β- hexosaminidase release and 86Rb+-efflux and their potency was as follows: UCL1608 > 1710 > 1617 > 1348 > 1349 > 1495. Charybdotoxin inhibited repolarisation and 86Rb+-efflux with a similar IC50 (~90nM) to that for inhibition of secretion. Margatoxin 10nM (Kv1.3 blocker) and tetraethyl ammonium 5mM (BKCa blocker) did not affect antigen-induced secretion significantly. Since charybdotoxin is capable of inhibiting BKCa, IKCa and Kv1.3, these results suggest that the outward rectifier channel in RBL cells may have some similarities to IKCa but not to BKCa or KV1.3. This is consistent with the known inhibitory effect of cetiedil and the UCL compounds on the IKCa channels in erythrocytes. Based on my 86Rb+-efflux studies, it can be proposed that the K+-efflux pathway cannot be entirely voltage-dependent and also that it may comprise two components, one Ca2+-dependent and the other Ca2+-independent. It can be concluded that at least two kinds of K+ channels are activated by antigen; Ca2+-independent (possibly G-protein-linked) channels whose activation is not necessary for degranulation and Ca2+-dependent channels which help to maintain the electrochemical driving force for Ca2+ influx.

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