P-C3-30 Model of cation channel gating

C3 Structure and function of ionic channels P-C3-29

P-C3-30

TWWE Dk’XNCT GATING MODES COl’i’iltOL CYCLIC NUCLEOTIDE-GATED CHANNELS SESI’I F; EISMANN E; PRINGS s; KAUPP U.B.

MODEL OF CATION CqANNEL GATING BURYl V.A. ’ MOREL N; GODFRAIND T,’

Institut tir Biologische Iofonnationsvemrbcitung, ForschungszentrumJUllch,Germany Purpose:

We

have

investigated

the

gating

mechanisms in cyclic nucleotlde-gated (CNG) channels by measuring the contribution of membrane voltage, binding of permeating ions and binding of cGMP to the regulation of open probability (p,). Methods: The a-subunit of bovine rod CNG channels as well as severalchannel mutants were expressed in Xenopus oocytes and studied by patch-clamp techniques. Results: Under conditions of reduced ion binding within the pore, the channels display properties typical of voltage-gated channels: inactivation and voltage dependenceof pw Conclusions: CNG channels sense and respond to changes in membrane voltage. Under physiological conditions, however, permeating ions suppressvoltage effects on gating so that p0 is almost exclusively determined by the cGMP concentration.

P-C3-32

P-c3-3 1

PROTONATION OF PORE GLUTAMATES CONTROLS Ca” PERMEATION IN CNG CHANNELS.

VENEGAS-COTERO B&n’,REEOLLEDO S’z ORPEGA-BLAEE P-1.SAINT-MARTIN II*.>.

SEIFERT

Purpose: Studies of antrbiottc ionophores are important for urtderstanding the basic feature5 of tranamembrane ionic channels. and for their possible manipulation for pharsko~ogical use. Amphotericine B makes channels with interesting transrnembrane properties and is used against micotic infections. in snite of its noxi&a collateral efiects. The &ucture of the channel Cte rids on the type of sterol resent in the memr rane so this feature might4 tfferentiate its action on human and fun al cells. In this work we look into the effects of sterols and temperature on the single channel properties, becauseboth nre known to modify the properties of the membmne. Methods: Stan&u-d &&-channel recording techniques are wed to measure the amphoteritine B channel properties. Results: We found that the properties of chan- ’ nels in both sterol-containing and sterol-free membranes are the same. Thi; su gests the acthe ionic channel to be fdue to on the membrane. The studsterol-free membranes at various temper&urea@tppart thii interpretation. C~n&sbnfs?

The

r@iiW

suggest

that

R. EISMANN

E, DZUA

C, KAUPP

UB.

Inst.Biol.Inform.Verarbeitung, Jiilich(D),

Uaiv. Aut. Edo. hiorelos, C!~&ca MEX) ‘Institute de F&a, uNAM,$ueywca (ME d ) ‘F. C.

the for-

mation and fun&~ of the channei are strongly related to stmcturdmembrane properties and that the putative involvement of sterol is due tn t.lliS mrrlrRni~m

113

Purpose: Cyclic nucleotide-gated (CNG) channels from rod and cone photoreceptor cells differ remarkably in their Ca2’ permeation properties, which could account for differences in light sensitivity and adaptation. TO understandthe molecular basis of Ca” permeability, we investigated CNG channel currents, Ca2’ block and fractional Ca2’ cumnts at various pH. Methods: Bovine rod and cone CNG channels were expressedin Xenopus oocytes or HEK 293 cells. Currents were measured in the presenceof different [Ca2’], and pH in the outside-out patchclamp configuration. Fractional Ca2’ currents were determined by simultaneously measuring whole-cell currents and NRA-2 fluorescence. Results: K’ current through CNG channels is strongly inhibited at low pH, whereas the block by [Ca2’], is alleviated. Differences in the protonation of pore glutamates in rod and cone CNG channels are observed. The fractional Ca2’ current is also controlled by pH. Conclusions: The different degree of protonation of pore glutamates in rod and cone CNG channels account, at least in part, for their distinct Ca2’ permeation and Ca2’ blockage.