Effect of bradykinin, ATP and adrenaline on cell membrane resistances of Madin-Darby canine kidney cells

Integration of intracellular signaling: Biological analogues of wires, processors and memories organized by a centrosome 3D reference system

BACKGROUND

Myriads of signaling pathways in a single cell function to achieve the highest spatio-temporal integration. Data are accumulating on the role of electromechanical soliton-like waves in signal transduction processes. Theoretical studies strongly suggest feasibility of both classical and quantum computing involving microtubules.

AIM

A theoretical study of the role of the complex composed of the plasma membrane and the microtubule-based cytoskeleton as a system that transmits, stores and processes information.

METHODS

Theoretical analysis presented here refers to (i) the Penrose-Hameroff theory of consciousness (Orchestrated Objective Reduction; Orch OR), (ii) the description of the centrosome as a reference system for construction of the 3D map of the cell proposed by Regolini, (iii) the Heimburg-Jackson model of the nerve pulse propagation along axons' lipid bilayer as soliton-like electro-mechanical waves.

RESULTS AND CONCLUSION

The ideas presented in this paper provide a qualitative model for the decision-making processes in a living cell undergoing a differentiation process.

OUTLOOK

This paper paves the way for the real-time live-cell observation of information processing by microtubule-based cytoskeleton and cell fate decision making.

Ruled by waves? Intracellular and intercellular calcium signalling

The field of calcium signalling has evolved rapidly the last 20 years. Physiologists had worked with cytosolic Ca2+ as the coupler of excitation and contraction of muscles and as a secretory signal in exocrine glands and in the synapses of the brain for several decades before the discovery of cellular calcium as a second messenger. Development of powerful techniques for measuring the concentration of cytosolic free calcium ions in cell suspensions and later in single cells and even in different cellular compartments, has resulted in an upsurge in the knowledge of the cellular machinery involved in intracellular calcium signalling. However, the focus on intracellular mechanisms might have led this field of study away from physiology. During the last few years there is an increasing evidence for an important role of calcium also as an intercellular signal. Via gap junctions calcium is able to co-ordinate cell populations and even organs like the liver. Here we will give an overview of the general mechanisms of intracellular calcium signalling, and then review the recent data on intercellular calcium signals. A functional coupling of cells in different tissues and organs by the way of calcium might be an important mechanism for controlling and synchronizing physiological responses

Bradykinin-evoked Ca2+ mobilization in Madin Darby canine kidney cells

We studied the mechanisms underlying the bradykinin-evoked changes in intracellular calcium concentration ([Ca2+]i) in Madin Darby canine kidney (MDCK) cells. Bradykinin evoked a [Ca2+]i transient in a dose-dependent manner, measured by fura-2 fluorimetry and digital video imaging. The transient consisted of a rise and a decay and [Ca2+]i returned to baseline without oscillations. External Ca2+ influx occurred, as demonstrated by Mn2+ quench and external Ca2+ removal measurements. Bradykinin acted by stimulating bradykinin B2 receptors as evidenced by blockade by D-arginyl-L-arginlyl-L-prolyl-trans-4-hydroxy-L-prolylglycyl -3-(2-thienyl)-L-alanyl-L-seryl-D-1,2,3,4-tetrahydro-3-isoquinolineca rbonyl-L-(2alpha,3beta,7alphabeta)-octahydro-1 H-indole-2-carbonyl-L-arginine (HOE 140) but not by D-arginyl-L-arginlyl-L-prolyl-trans-4-hydroxy-L-proylglycyl- 3-(2-thienyl)-L-alanyl-L-seryl-D-1,2,3,4-tetrahydro-3-isoquinolinecar bonyl-L-(2alpha,3beta,7alphabeta)-octahydro-1 H-indole-2-carbonyl ([Des-Arg]HOE 140). The [Ca2+]i signal was abolished by 1-(6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1 H-pyrrole-2,5-dione (U73122) and partially inhibited by neomycin, implying mediation by phospholipase C. The transient was initiated by a release of Ca2+ from internal stores since it was abolished by pretreatment with thapsigargin or cyclopiazonic acid. The mobilization of the internal Ca2+ store subsequently triggered a 1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1 H-imidazole hydrochloride (SKF 96365)-insensitive Ca2+ entry. Pretreatment with carbonylcyanide m-chlorophynylhydrozone and gly-phe-beta-naphthylamide did not alter the transient, thus excluding the participation of mitochondria and lysosomes. Efflux via Ca2+ pumps contributed to the decay of the transient. Efflux via Na+/Ca2+ exchange or sequestration by mitochondria and lysosomes was insignificant. The transient was blunted by the protein kinase C activator phorbol 12-myristate 13-acetate, and was enhanced by the protein kinase C inhibitors sphingosine and chelerythrine, the protein kinase A inhibitor 2,5-di-(t-butyl)-1,4-hydroquinone, N-[2-(p-bromocinnamylamino)ethyl]5-isoquinolinesulfonamide (H-89), the agent 8-(diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB-8), and agents that elevated levels of 3',5'-cyclic guanosine monophosphate. The transient did not heterologously desensitize with that evoked by ATP, ADP or UTP.

Synchronized Ca2+ oscillations induced in Madin Darby canine kidney cells by bradykinin and thrombin but not by ATP

In an earlier report, we described synchronous Ca2+ oscillations in globally stimulated, subconfluent MDCK cells [Røttingen J-A, Enden T., Camerer E., Iversen J-G., Prydz H. Binding of human factor VIIa to tissue factor induces cytosolic Ca2+ signals in J82 cells, transfected COS-1 cells, Madin-Darby canine kidney cells and in human endothelial cells induced to synthesize tissue factor. J Biol Chem 1995; 270: 4650-4660]. In order to elucidate the mechanisms behind these oscillations, we have analyzed the fluctuations in cytosolic Ca2+ in single, Fura-2 loaded, MDCK cells grown to subconfluence, after stimulation with bradykinin, thrombin and ATP. All three agonists gave rise to an initial Ca2+ spike followed by oscillations or transients. Both the initial and subsequent spikes appeared to be due mainly to release of Ca2+ from internal stores, since they remained after Ca2+ influx was impeded by either La3+ or by chelation of extracellular Ca2+ with EGTA. The secondary spikes were apparently synchronized when the cells were (permanently and globally) stimulated with bradykinin or thrombin, but each cell seemed to oscillate independently when stimulated in the same way with ATP. Synchronized secondary spikes arose with a constant frequency and amplitude, independent of agonist concentration in contrast to most Ca2+ oscillations observed. Pretreatment of the cells with octanol to block gap junctions, or with EGTA or La3+ to inhibit Ca2+ influx, abolished the synchronization induced by bradykinin or thrombin. We observed that in the MDCK cell layer there are some "pacemaker' cells and hypothesize that these have a higher sensitivity for the agonists than their neighboring cells. From these pacemakers, an intercellular Ca2+ wave can be seen to spread to adjacent cells in the presence of intact gap junctions, thereby initiating concurrent transients in all cells. The Ca2+ wave is amplified by release from internal stores, probably owing to the bell-shaped Ca2+ activation curve of the IP3 receptor and by subsequent Ca2+ influx through Ca2+ release activated channels.

Properties and regulation of ion channels in MDCK cells

The MDCK cell has proven to be a useful model cell line for the study of properties and regulation of renal epithelial ion channels. Patch clamp studies disclosed the existence of several K+ channels and of a Cl- channel, and their regulation by hormones, cell volume, trace elements and drugs. Most hormones affect K+ channels at least in part by increasing cytosolic Ca2+. However, indirect evidence points to additional mechanisms contributing to K+ channel activation. Cell swelling activates both K+ channels and unselective anion channels. ICln, a protein cloned from MDCK cells, is either a Cl- channel or a regulator of thereof. ICln is up-regulated by cellular acidification and is crucial for rapid regulatory cell volume decrease.

Cell shrinkage stimulates bradykinin-induced cell membrane potential oscillations in NIH 3T3 fibroblasts expressing the ras-oncogene

In NIH 3T3 fibroblasts expressing the Ha-ras oncogene (+ ras) bradykinin leads to sustained oscillations of cell membrane potential due to oscillations of intracellular Ca2+ with subsequent activation of Ca(2+)-sensitive K+ channels. In cells not expressing the oncogene (-ras), bradykinin leads only to a single transient hyperpolarization of the cell membrane. The present study has been performed to elucidate the possible interaction of cell volume, intracellular pH and bradykinin-induced oscillations of the cell membrane potential. Bradykinin leads to cell shrinkage and intracellular alkalinization of both + ras cells and -ras cells. Inhibition of Na+/H+ exchanger by HOE 694 abolishes the bradykinin-induced alkalinization but does not significantly interfere with the bradykinin-induced oscillations of cell membrane potential. In contrast, prevention of bradykinin-induced cell shrinkage by simultaneous reduction of extracellular osmolarity blunts the oscillations. Thus, cell shrinkage stimulates bradykinin-induced oscillations of cell membrane potential. On the other hand, cell shrinkage alone does not elicit oscillations unless, in addition, Ca2+ entry is stimulated by ionomycin.

Bradykinin stimulation of electrogenic ion transport in epithelial layers of cultured human endometrium

Primary cultures of glandular endometrial epithelial cells grown on permeable supports formed monolayers with a high transepithelial electrical resistance [1096 +/- 83 omega.cm2 (n = 34)] and displayed electrogenic ion transport as demonstrated by an inward short circuit current (Isc; 20 +/- 2 microA/cm2). Bradykinin, 10(-8)-10(-6) M, added to either the basolateral or apical solutions enhanced the inward ISC. The concentration-response curves for bradykinin were bell-shaped in nature. The ISC response was more sensitive to apical addition of bradykinin and the maximum response was also greater with apical bradykinin. The increases in ISC were accompanied by two- to three-fold increases in transepithelial conductance. Apical addition of amiloride, 10(-4) M, reduced the unstimulated ISC by 80%. In the presence of amiloride, the response to both apical and basolateral bradykinin was reduced by > 50% in 8 out of 18 layers, and the mean response was reduced by approximately 25%. The data are consistent with a physiological role for bradykinin in the control of the intrauterine electrolyte environment, mediated in part by enhanced Na+ absorption.

Effects of bradykinin on cell volume and intracellular pH in NIH 3T3 fibroblasts expressing the ras oncogene

BCECF fluorescence has been applied to determine intracellular pH (pHi) in NIH 3T3 fibroblasts expressing the Ha-ras oncogene (+ras) and otherwise identical cells not expressing the oncogene (-ras). In +ras cells, pHi is significantly more alkaline (6.79 +/- 0.03 n = 12) than in -ras cells (6.64 +/- 0.02, n = 8). Bradykinin (100 nmol/l) leads to intracellular alkalinization in both +ras (to 6.96 +/- 0.04, n = 12) and -ras cells (to 6.85 +/- 0.02, n = 8). The effect of bradykinin is completely abolished in the presence of dimethylamiloride (100 mumol/l), which does not modify pHi in the absence of bradykinin. Similar to bradykinin, cell shrinkage by addition of 15 mmol/l NaCl to the extracellular fluid leads to intracellular alkalinization (by 0.08 +/- 0.01, n = 15). Cell volume is significantly greater in +ras cells (2.7 +/- 0.4 pl, n = 15) than in -ras cells (2.2 +/- 0.4 pl, n = 15). Bradykinin leads to cell shrinkage in both +ras cells (by 7 +/- 1%, n = 17) and -ras cells (by 5 +/- 1%, n = 15). The effect of bradykinin on cell volume can be reversed by the reduction of extracellular NaCl concentration by 15 mmol/l NaCl in +ras cells and by 7 mmol/l NaCl in -ras cells. This maneuver completely abolishes (in -ras cells) or blunts (in +ras cells) the alkalinizing effect of bradykinin. In conclusion, +ras cells are more alkaline than -ras cells. Bradykinin leads to further intracellular alkalinization by activation of the Na+/H(+)-exchanger, at least in part secondary to hormone-induced cell shrinkage.