Skip to main content

Tonic and phasic activity in smooth muscle


We have studied the electrical and mechanical behaviour of two very different smooth muscle preparations, mesenteric lymphatic ducts and proximal urethra. These tissues generate different patterns of spontaneous contraction adapted to fulfil their contrasting functions. While lymphatics undergo regular phasic contractions and relaxations, suited to their role in propelling lymph, the urethra remains in a state of contracture to maintain urinary continence. The challenge is to understand how both of these achieve their respective roles.

Interestingly, electrical activity of lymphatics resembles that in the heart in having a one to one relationship between the action potential and phasic contraction. Patch clamp studies have shown that lymphatic cells express 3 ionic currents that are not present in urethral cells, but are shared with cardiac muscle. These are, i) fast Na+ current, ii) T-type Ca2+ current and iii) a hyperpolarisation-activated cation current, If. The fast Na+ current is ideally suited to the propagation of the action potential over large distances, as required by a vessel capable of generating a rapid well co-ordinated contraction along its length. The T-current and If, on the other hand, appear to be involved in electrical pacemaking as they are in the heart.

The urethra does not usually undergo regular phasic contractions and it lacks these currents. Instead, urethral tone may depend on an interaction between L-type Ca2+ current and a large Ca2+-activated Cl current. Activation of Cl channels (perhaps by spontaneous release of Ca2+ from intracellular stores) would depolarise the membrane potential to within the ‘window current’ range for L-type Ca2+ channels and result in Ca2+ influx and contraction. This process may be maintained for a time by positive feedback whereby the influx of Ca2+ continues to activate the Cl channels.

This is a preview of subscription content, access via your institution.


  1. Maizels, M. 1969. Biographical Memoirs of Fellows of the Royal Society, 1969; 15: 69–82.

    Article  CAS  Google Scholar 

  2. McHale, N. G., Roddie, I. C., Thornbury, K. D. Nervous modulation of spontaneous contractions in bovine mesenteric lymphatics. J. Physiol. 1980; 309: 461–472.

    PubMed  CAS  Google Scholar 

  3. Hollywood, M. A., McHale, N. G. Mediation of excitatory neurotransmission by the release of ATP and noradrenaline in sheep mesenteric lymphatic vessels. J. Physiol. 1994; 481: 415–423.

    PubMed  CAS  Google Scholar 

  4. Thornbury, K. D., Hollywood, M. A., McHale, N. G. Mediation by nitric oxide of neurogenic relaxation of the urinary bladder neck muscle in sheep. J. Physiol. 1992; 451: 133–144.

    PubMed  CAS  Google Scholar 

  5. Allen, J. M., McHale, N. G., Rooney, B. M. Effect of norepinephrine on contractility of isolated mesenteric lymphatics Am. J. Physiol. 1983: 244: H479-H486.

    PubMed  CAS  Google Scholar 

  6. Ward, S. M., Sanders, K. M., Thornbury, K. D., McHale, N. G. Spontaneous electrical-activity in isolated bovine lymphatics recorded by intracellular microelectrodes. J. Physiol. 1991; 438: 168.

    Google Scholar 

  7. Callahan, S. M., Creed, K. E. The effects of oestrogens on spontaneous activity and responses to phenylephrine of the mammalian urethra. J. Physiol. 1985: 358: 35–46.

    PubMed  CAS  Google Scholar 

  8. Ito, Y., Kimoto, Y. The neural and non-neural mechanisms involved in urethral activity in rabbits. J. Physiol. 1985; 367: 57–72.

    PubMed  CAS  Google Scholar 

  9. Creed, K. E., Oike, M., Ito, Y. The electrical properties and responses to nerve stimulation of the proximal urethra of the male rabbit. Br. J. Urol. 1997; 79, 543–553.

    PubMed  CAS  Google Scholar 

  10. Cotton, K. D., Hollywood, M. A., McHale, N. G., Thornbury, K. D. Ca2+-current and Ca2+-activated chloride current in isolated smooth muscle cells of the sheep urethra. J. Physiol. 1997; 505.1: 121–131.

    Article  Google Scholar 

  11. Hollywood, M. A., Toland, H. M., Cotton, K. D., Thornbury, K. D., McHale, N. G. Characterisation of a calciumactivated chloride current in isolated sheep lymphatic smooth muscle cells. J. Physiol. 1997, 505: 97P.

  12. Boyle, P. J., Conway, E. J. Potassium accumulation in muscle and associated changes. J. Physiol. 1941; 100, 1–63.

    PubMed  CAS  Google Scholar 

  13. Barchi, R. L. Ion channel mutations and diseases of skeletal muscle. Neurobiology of Disease 1997; 4: 254–264.

    PubMed  Article  CAS  Google Scholar 

  14. Aicken, C. C., Brading, A. F. The role of chloridebicarbonate exchange in the regulation of intracellular chloride in guinea-pig vas deferens. J. Physiol. 1984; 349: 587–606.

    Google Scholar 

  15. Aicken, C. C., Brading, A. F. The effect of loop diuretics on Cl-transport in smooth-muscle of the guinea-pig vasdeferens and taenia from the caecum. J. Physiol 1990; 421: 33–53.

    Google Scholar 

  16. Davis, J. P. L. Evidence against a contribution by Na+ Cl cotransport to chloride accumulation in rat arterial smooth muscle. J. Physiol. 1996; 491: 61–68.

    PubMed  CAS  Google Scholar 

  17. Large, W. A. & Wang, Q. Characteristics and physiological role of the Ca2+-activated Clconductance in smooth muscle. Am. J. Physiol. 1996; 271: C435-C454.

    PubMed  CAS  Google Scholar 

  18. Van Helden, D. F. Pacemaker potentials in lymphatic smooth muscle of the guinea-pig mesentery. J. Physiol. 1993; 471: 465–479.

    PubMed  Google Scholar 

  19. Hashitani, H., Van Helden, D. F., Suzuki, H. Properties of depolarizations in circular smooth muscle cells of rabbit urethra. Brit. J. Pharmacol. 1996; 118 (7): 1627–1632.

    CAS  Google Scholar 

  20. Hagiwara, N., Irisawa, H., Kameyama, M. Contribution of two types of calcium current to the pacemaker potentials of rabbit sino-atrial node cells. J. Physiol. 1988; 395: 233–253.

    PubMed  CAS  Google Scholar 

  21. Hollywood, M. A., Cotton, K. D., Thornbury, K. D., McHale, N. G. Isolated sheep mesenteric lymphatic smooth muscle cells possess both T-and L-type calcium currents. J. Physiol. 1997; 501: 109P.

  22. McHale, N. G., Roddie, I. C. The effect of transmural pressure on pumping activity in isolated bovine mesenteric lymphatic vessels. J. Physiol. 1976; 261: 255–269.

    PubMed  CAS  Google Scholar 

  23. Convery, M. C., Hollywood, M. A., Cotton, K. D., Thornbury, K. D., McHale, N. G. Role of inward currents in pumping activity of isolated sheep lymphatics. J. Physiol. 1997; 501: 110–111P.

    Google Scholar 

  24. DiFrancesco, D. The cardiac hyperpolarizing-activated current, If, origins and developments. Prog. Biophys. molec. Biol. 1985; 46: 163–183.

    Article  CAS  Google Scholar 

  25. Denyer, J. C., Brown, H. F. Pacemaking in rabbit isolated sino-atrial node cells during Cs+ block of the hyperpolarization-activated current, If. J. Physiol. 1990; 429: 401–409.

    PubMed  CAS  Google Scholar 

  26. Cotton, K. D., Toland, H. M., Hollywood, M. A., Thornbury, K. D., McHale, N. G. Characterisation of a hyperpolarization-activated current in isolated sheep mesenteric lymphatic smooth muscle cells. J. Physiol. 1998 (in press).

  27. Hollywood, M. A., Cotton, K. D., Thornbury, K. D., McHale, N. G. Tetrodotoxin-sensitive sodium current in sheep lymphatic smooth muscle. J. Physiol. 1997; 503.1: 13–20.

    Article  Google Scholar 

  28. Bramich, N. J., Brading, A. F. Electrical properties of smooth muscle in the guinea-pig urinary bladder. J. Physiol. 492.1: 185–198.

Download references

Author information

Authors and Affiliations


Additional information

Conway Review Lecture

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Thornbury, K.D. Tonic and phasic activity in smooth muscle. Ir. J. Med. Sc. 168, 201–207 (1999).

Download citation

  • Issue Date:

  • DOI:


  • Spontaneous Contraction
  • Niflumic Acid
  • Pacemaker Potential
  • Smooth Muscle Preparation
  • Sinoatrial Node Cell