phenylamil and 3--4--dichlorobenzamil

Dichlorobenzamil, phenamil and other amiloride analogs (1-100 microM) elicit transient tension in rabbit skinned muscle fibers. Tension requires preloading of Ca(2+) into the sarcoplasmic reticulum, is facilitated by low-[Mg(2+)] solutions, abolished by ruthenium red or by functional disruption of the sarcoplasmic reticulum, and is followed by inhibition of the caffeine-evoked tension. Bilayer recording of Cs(+) currents through the sarcoplasmic reticulum Ca(2+) release channel reveals that phenamil (10-100 microM) increases the open channel probability, whereas dichlorobenzamil affects the channel activity in a complex concentration- and time-dependent manner: stimulation occurs throughout exposure to 10 microM, but is followed by channel blockade when 100 microM dichlorobenzamil is used. It is concluded that stimulation of the sarcoplasmic reticulum Ca(2+) release channel accounts for the dichlorobenzamil- or phenamil-induced tension in skinned fibers, whereas depletion of sarcoplasmic reticulum Ca(2+) stores and channel block (with dichlorobenzamil) explains the inhibition of the caffeine-evoked tension by amiloride analogs.

Topics: Amiloride; Animals; Caffeine; Calcium; Calcium Channels; Cetomacrogol; Diuretics; Electrophysiology; In Vitro Techniques; Isometric Contraction; Magnesium; Membranes; Muscle Fibers, Skeletal; Phosphodiesterase Inhibitors; Rabbits; Ruthenium Red; Ryanodine Receptor Calcium Release Channel; Sarcoplasmic Reticulum; Sodium Channels; Solutions

1. Smooth muscle cells were dispersed from rat aorta and then cultured. The action of palytoxin on rat aortic myocytes was analysed by measurement of 22Na+ uptake and single channel recording techniques. 2. Palytoxin induced an increase in 22Na+ uptake, with a concentration of 50 nM producing half-maximal activation. The action of palytoxin was inhibited by amiloride derivatives and by ouabain. The concentrations of inhibitor producing half-maximal inhibition were 10 microM for 3,4 dichlorobenzamil, 30 microM for benzamil, 100 microM for phenamil and 1 mM for ouabain. 3. In outside-out patches, palytoxin induced single channel currents that reversed near 0 mV with NaCl or KCl in the extracellular solution, but were outward with N-methyl-D-glucamine chloride or CaCl2 (110 mM), indicating that palytoxin induced a cation channel permeable to Na+ and K+ (PK/PNa = 1.2) but not to Ca2+ (PK/PCa > 30) or to N-methyl-D-glucamine (NMDG) (PK/PNMDG > 11) The unit channel conductance was 11-14 pS. 4. A high (> 0.1 mM) extracellular concentration of Ca2+ was necessary to observe channel activation by palytoxin. A high (150 mM) extracellular concentration of K+ partially prevented and reversed channel activation by palytoxin. 5. The channel activity was fully blocked by 3,4 dichlorobenzamil (20 microM) and partially blocked by phenamil (50 microM). It was not reduced by ouabain (200 microM).

Topics: Acrylamides; Amiloride; Animals; Aorta, Thoracic; Calcium; Cells, Cultured; Cnidarian Venoms; Electrophysiology; In Vitro Techniques; Ion Channels; Muscle, Smooth, Vascular; Ouabain; Potassium; Rats; Rats, Wistar; Sodium; Sodium Channels; Sodium Radioisotopes

The Na+ transport inhibitor amiloride blocks taste responses to NaCl by 60-70%. The purpose of the present study was to determine if greater inhibition could be achieved with three potent amiloride analogs that are specific for the epithelial Na+ channel: phenamil, 2',4'-dimethylbenzamil, and 3',4'-dichlorobenzamil. Application of phenamil (100 microM) to the anterior tongue blocked integrated responses to NaCl from the chorda tympani nerve by 98.04%, but had no significant effect on sucrose or NH4Cl. This finding suggests that the epithelial Na+ channel alone transduces the taste of NaCl in gerbil. The residual 30-40% of the response that is not blocked by amiloride can simply be explained by the fact that amiloride is less potent than phenamil. On average, 100 microM phenamil blocked responses to Na+ salts with a variety of anions by 94.2%; 100 microM 2',4'-dimethylbenzamil, by 89.83%; and 100 microM 3',4'-dichlorobenzamil, by 72.56%. Small residual responses to salts of glutamate and phosphate were not eliminated by the amiloride analogs; this suggests that other transduction mechanisms may account for a small portion of taste responses for these salts in the gerbil.

Topics: Amiloride; Animals; Electrophysiology; Epithelium; Female; Gerbillinae; Sodium; Sodium Channels; Taste

The potency of several amiloride analogues to inhibit electrogenic Na+ transport in colon from dexamethasone-treated rats was compared. Short-circuit current (Isc) across the colonic mucosa and 22Na+ uptake into membrane vesicles derived from colonic enterocytes was determined in dexamethasone-treated rats. Kinetic analysis of inhibition of Isc and 22Na+ uptake revealed the presence of a high- and low-affinity amiloride pathway. One pathway had a high affinity [(Ki-Isc; Ki uptake] to benzamil (15.5 nM; 5.4 nM), phenamil (19.4 nM; 7.0 nM), 3',4'-dichlorobenzamil (29.0 nM; 25.2 nM), and amiloride (115 nM; 12.4 nM) but a much lower affinity to 5-(N-ethyl-N-isopropyl)amiloride (EIPA) (greater than 100 microM; greater than 9.9 microM) and 5-(N-propyl-N-butyl)-2'-4'-dichlorobenzamil (PBDCB) (greater than microM; greater than 32.8 microM). The high-affinity pathway accounted for 75-83% of the transport of Na+. The second pathway had nearly the same low affinity for each of the analogues (e.g., amiloride Ki-Isc 1 microM; Ki uptake 4 microM) and accounted for only 15-25% of the transport of Na+. The results demonstrate that the structure-inhibitory pattern of these amiloride analogues for the high-affinity pathway is the pattern observed in other electrogenic Na+-transporting epithelia and that this pharmacological profile is preserved in membrane vesicles derived from colonic enterocytes. In addition, the potency of EIPA and benzamil to inhibit electroneutral Na+ transport across the colon from normal rats (i.e., not treated with dexamethasone) was also investigated.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Amiloride; Animals; Biological Transport; Colon; Dexamethasone; Electric Conductivity; Electrophysiology; Epithelium; Female; Kinetics; Rats; Rats, Inbred Strains; Sodium