Thapsigargin, a Ca(2+)-ATPase inhibitor, relaxes guinea pig tracheal smooth muscle by producing epithelium-dependent relaxing factors

Pharmacological modulation of sarcoplasmic reticulum function in smooth muscle

The sarco/endoplasmic reticulum (SR/ER) is the primary storage and release site of intracellular calcium (Ca2+) in many excitable cells. The SR is a tubular network, which in smooth muscle (SM) cells distributes close to cellular periphery (superficial SR) and in deeper aspects of the cell (deep SR). Recent attention has focused on the regulation of cell function by the superficial SR, which can act as a buffer and also as a regulator of membrane channels and transporters. Ca2+ is released from the SR via two types of ionic channels [ryanodine- and inositol 1,4,5-trisphosphate-gated], whereas accumulation from thecytoplasm occurs exclusively by an energy-dependent sarco-endoplasmic reticulum Ca2+-ATPase pump (SERCA). Within the SR, Ca2+ is bound to various storage proteins. Emerging evidence also suggests that the perinuclear portion of the SR may play an important role in nuclear transcription. In this review, we detail the pharmacology of agents that alter the functions of Ca2+ release channels and of SERCA. We describe their use and selectivity and indicate the concentrations used in investigating various SM preparations. Important aspects of cell regulation and excitation-contractile activity coupling in SM have been uncovered through the use of such activators and inhibitors of processes that determine SR function. Likewise, they were instrumental in the recent finding of an interaction of the SR with other cellular organelles such as mitochondria. Thus, an appreciation of the pharmacology and selectivity of agents that interfere with SR function in SM has greatly assisted in unveiling the multifaceted nature of the SR.

Effect of flavonoids from various Mediterranean plants on enzymatic activity of intestinal carboxylesterase

Flavonol compounds of three Mediterranean plants from the Algerian Atlas used traditionally in Arab folk medicine, Arenaria serpyllifolia, Rhamnus alaternus and Thapsia garganica, were found to inhibit the enzymatic activities of both rat intestine and purified porcine liver carboxylesterase in a concentration-dependent manner. Results indicate that the flavonol compounds from the aerial part of these plants lead to the inactivation of the CE pI = 5.1 with Ki of micromolar range. These results encourage us to perform further biological investigation.

Effects of ionomycin and thapsigargin on ion currents in oocytes of Bufo arenarum

In this study, two electrode voltage clamp technique was used to assess the ionic current of oocytes of the South American toad Bufo arenarum and to study the dependence of these currents on the extracellular and intracellular Ca2+ concentrations. Ca2+ chelators, ionomycin -a calcium ionophore- and thapsigargin, a blocker of the Ca2+ pump of the sarcoplasmic reticulum, were used. The main results were the following: Most oocytes showed a voltage activated rectifying conductance. Ionomycin (1 microM) increased inward and outward currents in control solution. The effect of ionomycin was blocked partially at negative potentials and was blocked completely at positive potentials in absence of extracellular Ca2+. When the oocytes were treated with thapsigargin (2 microM) or BAPTA-am, a membrane-permeant intracellular chelator in control solution (10 microM), ionomycin did not increased either inward nor outward currents. The conclusion of our experiments is that there are two sources of Ca2+ for activation of the current induced by ionomycin, the cytoplasmic stores and the extracellular space. We believe ionomycin directly translocates Ca2+ from the SER into the cytoplasm but not from the extracellular medium. Ca2+ entry probably occurs through store-operated-Ca-channels.

Mucus secretion from single submucosal glands of pig. Stimulation by carbachol and vasoactive intestinal peptide

Secretion rates of >700 individual glands in isolated tracheal mucosa from 56 adult pigs were monitored optically. "Basal" secretion of 0.7 +/- 0.1 nl x min(-1) gland(-1) was observed 1-9 h post-harvest but was near zero on day 2. Secretion to carbachol (10 microm) peaked at 2-3 min and then declined to a sustained phase. Peak secretion was 12.4 +/- 1.1 nl x min(-1) gland(-1); sustained secretion was approximately one-third of peak secretion. Thapsigargin (1 microm) increased secretion from 0.1 +/- 0.05 to 0.7 +/- 0.2 nl x min(-1) gland(-1); thapsigargin did not cause contraction of the trachealis muscles. Isoproterenol and phenylephrine (10 microm each) were ineffective, but vasoactive intestinal peptide (1 microm) and forskolin (10 microm) each produced sustained secretion of 1.0 +/- 0.5 and 1.7 +/- 0.2 nl x min(-1) gland(-1), respectively. The density of actively secreting glands was 1.3/mm(2). Secretion to either carbachol or forskolin was inhibited (approximately 50%) by either bumetanide or HCO(3)(-) removal and inhibited approximately 90% by the combined treatments. Mucus secreted in response to carbachol or forskolin was acidic by approximately 0.2 pH units relative to the bath and remained acidic by approximately 0.1 pH units after bumetanide. The strong secretory response to vasoactive intestinal peptide, the acidity of [cAMP](i)-stimulated mucus, and its inhibition by bumetanide were unexpected.