Amiloride inhibits mammalian renal kallikrein and a kallikrein-like enzyme from toad bladder and skin.

Abstract

A B S T R A C T Renal kallikrein is localized in luminal plasma membranes of the mammalian distal nephron and gains access to urine from this site. Its activity is regulated, in part, by aldosterone. These facts led us to study the effects of amiloride, a drug known to inhibit sodium reabsorption and potassium secretion at this site, on kallikrein activity. Amiloride inhibited the esterolytic activity of purified rat or human urinary kallikrein or of rat renal cortical cells upon a synthetic substrate (ID50 = 0.12-0.23 mM). Kinetic analyses showed that the enzyme inhibition was noncompetitive and reversible in nature. The kinin-generating activity of kallikrein acting upon kininogen substrates was also inhibited by amiloride, as measured by bioassay in the rat uterus or guinea pig ileum or by radioimmunoassay of liberated kinins (ID50 = 85 A.tM). No other diuretic drug tested inhibited kallikrein activity, except triamterene, which did so, weakly. In addition, kallikrein-like enzyme activity was discovered in the urinary bladder or skin of Bufo marinus toads and this activity was also inhibited by amiloride. The localization ofthe enzyme and its inhibition by this drug suggest that further study of relationships amongst the glandular kallikrein-kinin system and renal ion and water transport is warranted.

Amiloride selectively inhibits the urokinase‐type plasminogen activator

“…This contention is supported by the fact that urinary kallikrein, a trypsin-like serine protease of similar catalytic specificity but with a different preferred 190 macromolecular substrate (i.e. kininogens), is also inhibited by both Na+ and amiloride [25,26]; however, it must be noted that inhibition of urinary kallikrein by amiloride is a controversial issue [27], and that the mode of kallikrein inhibition by amiloride was reported to be noncompetitive [25].…”

Kinins Stimulate Net Chloride Secretion by the Rat Colon

“…This conclusion now seems premature, as pointed out by Nishimura et al (1980), and since the concentration of bradykinin required to produce even a slight effect upon recovery of 22Na from the lumen of microinjected rat distal nephron segments is 500,000 times higher (Kauker, 1980) (Margolius & Chao, 1980) and that glandular kallikrein inhibitors decrease Na reabsorption by an action at apical plasma membrane sites in the amphibian urinary bladder (Orce et al, 1980;. Thus, kallikrein inhibition is associated with decreased Na reabsorption at some sites, but the kinin peptide products stimulate chloride secretion at another.…”

“…The activity of glandular kallikrein is increased by sodium-retaining steroid hormones (Geller, Mar-golius, Pisano & Keiser, 1972;Margolius, Horwitz, Geller, Alexander, Gill, Pisano & Keiser, 1974;Nasjletti, McGiff & Colina-Chourio, 1978;Nishimura, Alhenc-Gelas, White & Erdos, 1980). In addition, the mammalian glandular enzyme and a kallikreinlike enzymatic activity discovered in Bufo marinus bladder and skin are inhibited by amiloride (Margolius & Chao, 1980). This natriuretic and diuretic drug blocks sodium entry into a transport process in apical plasma membranes of tissues (renal distal nephron, salivary duct, colon) which contain high concentrations of kallikrein (for reviews, see Schachter, 1979;Cuthbert, Fanelli & Scriabine, 1979).…”

Role of the endogenous kallikrein-kinin system in modulating vasopressin-stimulated water flow and urea permeability in the toad urinary bladder.

“…Moreover, kallikrein has been shown to be located on the luminal membrane of the distal convoluted tubule and collecting duct of the mammalian nephron (7,8), the major site of vasopressin's action. An endogenous kallikrein-kinin system has also been identified in the toad urinary bladder (9,10), a close analogue of the mammalian distal nephron. Furthermore, Furtado (11) has reported that exogenous bradykinin decreases vasopressin-stimulated water flow in the amphibian urinary bladder.…”