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Plants Microbes Notes

Pharmacology Notes > BIOL10832 Excitable Cells Notes

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Excitable Cells in Plants And Microbes
Lecture 21 - Excitable Cells - 01/05/18
CHARACTERISTICS OF EXCITABLE CELLS:-

All possess a resting membrane potential (paramecium is about -40mV)
Involve regenerative ('all-or-none') action potentials
Have fast (short-lasting) signals - so that an organism responds to a stimulus and then doesn't carry on responding
Fast signal transmission (i.e. life and death decisions)
Signals must be related to changes in the environment and so there must be some way of transducing the signal from one form to another: e.g. touch/chemical →
electrical
Used for:
 Synchronising cells in a population
 Fast, purposeful and adaptive responses
 Decision-making

EVOLUTIONARY ORIGIN OF ION CHANNELS:-

Ion channels have their origins in prokaryotes
The earliest ion channels were probably K+
channels
Excitability depends on voltagegated cation channels (Ca2+ and
Na+)
Gene sequencing allows us to establish evolutionary relationships of channels
Na+ channels evolved from Ca2+ channels
Microbes and plants have their place in the story of excitability

MICROBES:
ION CHANNELS IN PROKARYOTES:No evidence that prokaryotic cells are excitable
Bacteria possess a wide range of ion channels (e.g. Na+, Cl-, Ca-gated K+, ionotropic glutamate receptors) with function largely unknown
There is evidence from biofilms that oscillations in membrane potential are due to K+
flux regulate waves of metabolic activity in bacterial populations
A study was done in 2016 where genetic engineering was used to express bacterial
Na+ channels in mammalian cells in vitro, Their function is unknown in bacteria but when they are expressed in mammalian cells they enhanced and restored excitability
- potential therapy for loss of function in nerve and muscle

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