Single-channel conductance

Fig. 4. A, Histogram of single channel conductances, y, of Gramicidin A in diphytanoyl L-a-lecithin/n-decane membranes for 1 M KC1, 130 mV potential and 40 °C. Note that single channel conductance is simply the single channel current, i , divided by the applied potential. Reproduced from reference 12) with permission.

C. Histogram of single channel conductances of Gramicidin A in glyceryl monoolein/hexadecane membranes for 1 M KC1, 103 mV applied potential and 23 °C. Reproduced with permission from Ref. 13>... 

CFTR has a single-channel conductance of about 8 pS. It is present in the apical membranes of many epithelia. Its mutation leads to the potentially lethal disease cystic fibrosis. In addition to acting as a chloride channel, CFTR is also thought to regulate, e.g., the epithelial sodium channel ENaC, a molecularly unknown outwardly-rectifying chloride channel, and possibly also potassium channels and water channels. Some of these potential regulatory processes, however, are controversial. CFTR also acts as a receptor for bacteria. 

Step 4 - Addition of the synthetic pardaxin (10 M) to the bath results after 10-20 min in tetramer insertion into the bilayer and pore formations as measured by the current fluctuations depicted in B at a positive potential of 100 mV. The single channel conductance can be estimated from the amplitude of the current steps divided by the applied voltage and was in the range of 10 pS. 

HT3 receptors are an exception to the general nomenclature of numbering subunits and denoting stoichiometry by subscripts. The 5-HT3 receptor subtype is denoted by the subscript 3 and the two known subunits are referred to as A and B . When expressed alone, 5-HT3-A subunits form functional homomeric receptors but these have a much smaller single channel conductance (less than 1.0 pS) and altered pharmacology compared to native 5-HT3 receptors. Native 5-HT3 receptors are likely to be pentameric heteromers of 5-HT3-A and 5-HT3-B subunits. 5-HT3-B subunits, unlike 5-HT3-A subunits, do not form functional receptors when expressed alone but when co-expressed with 5-HT3-A subunits, the receptors formed have functional properties similar to native 5-HT3 receptors. Synaptic transmission mediated by 5-HT3 receptors has been... 

Wotring, VE, Chang, Y and Weiss, DS (1999) Permeability and single channel conductance of human homomeric rhol GABAc receptors. J. Physiol. (Land.) 521 Part 2, 327-336. 

S5-S6 loop region in DRKl by the one of NGK2 confers to the recombinant channel the single-channel conductance and TEA sensitivity of NGK2 [47], Thus, a region of approximately twenty amino acids in the primary sequence of K channels controls essential properties of the K" channel pore [48]. 

Fig. 21.8. Frequency histograms of single-channel conductances for (A) SENS and (B) LEVR parasites. Gaussian curves were fitted to each distribution using the maximum likelihood procedure. The peaks for the SENS isolate were 21.4 + 2.3 pS (8% area) labelled G25 33.0 + 4.8 pS (31% area) labelled G35 38.1 + 1.2 pS (19% area) labelled G40 and 44.3 + 2.2 pS (42% area) labelled G45. The peaks for the LEVR isolate were 25.2 4.5 pS (21% area) labelled G25 41.2 1.7 pS (49% area) labelled G40 and 46.7 1.1 pS (30% area) labelled G45.

Bamberg and coworkers have studied the single channel conductance of gramicidins A, B and C80 81. Significant differences between gramicidin A and B were found. 

Peters JA, Garland JE, Cooper MA, Livesey MR, Deeb TZ, Hales TG, Lambert JJ (2006) Novel structural determinants of single-channel conductance in nicotinic acetylcholine and 5-hydroxytryptamine type-3 receptors. Biochem Soc Trans 34(5) 882-886 Picciotto MR, Zoli M, Rimondini R, Lena C, Marubio LM, Pich EM, Fuxe K, Changeux JP (1998) Acetylcholine receptors containing the beta2 subunit are involved in the reinforcing properties of nicotine. Nature 391 173-177... 

Subsequently the ion channel activity was tested by single-channel current measurements using planar lipid bilayers. Single-channel conductances of ca. 55 in 500 mM NaCl and 65 pS in KCl were obtained. The weak ion selectivity was claimed to reflect a slightly larger mobility of K compared to that of Na ion in bulk solution. Therefore a large 7.5-A pore structure in lipid bilayers is assumed to resemble the bulk aqueous solution. 

At least three types of disturbance in the intercellular communication have to be distinguished (1) separation of the cardiac muscle fibers by strands of connective tissue as occurring in microfibrosis (2) changes in the distribution of gap junction channels, and (3) changes in the conductance of gap junctional channels either by alteration of the open probability or of the single channel conductance. 

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